linux/kernel/cgroup.c
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   1/*
   2 *  Generic process-grouping system.
   3 *
   4 *  Based originally on the cpuset system, extracted by Paul Menage
   5 *  Copyright (C) 2006 Google, Inc
   6 *
   7 *  Notifications support
   8 *  Copyright (C) 2009 Nokia Corporation
   9 *  Author: Kirill A. Shutemov
  10 *
  11 *  Copyright notices from the original cpuset code:
  12 *  --------------------------------------------------
  13 *  Copyright (C) 2003 BULL SA.
  14 *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
  15 *
  16 *  Portions derived from Patrick Mochel's sysfs code.
  17 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
  18 *
  19 *  2003-10-10 Written by Simon Derr.
  20 *  2003-10-22 Updates by Stephen Hemminger.
  21 *  2004 May-July Rework by Paul Jackson.
  22 *  ---------------------------------------------------
  23 *
  24 *  This file is subject to the terms and conditions of the GNU General Public
  25 *  License.  See the file COPYING in the main directory of the Linux
  26 *  distribution for more details.
  27 */
  28
  29#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  30
  31#include <linux/cgroup.h>
  32#include <linux/cred.h>
  33#include <linux/ctype.h>
  34#include <linux/errno.h>
  35#include <linux/init_task.h>
  36#include <linux/kernel.h>
  37#include <linux/list.h>
  38#include <linux/magic.h>
  39#include <linux/mm.h>
  40#include <linux/mutex.h>
  41#include <linux/mount.h>
  42#include <linux/pagemap.h>
  43#include <linux/proc_fs.h>
  44#include <linux/rcupdate.h>
  45#include <linux/sched.h>
  46#include <linux/slab.h>
  47#include <linux/spinlock.h>
  48#include <linux/percpu-rwsem.h>
  49#include <linux/string.h>
  50#include <linux/sort.h>
  51#include <linux/kmod.h>
  52#include <linux/delayacct.h>
  53#include <linux/cgroupstats.h>
  54#include <linux/hashtable.h>
  55#include <linux/pid_namespace.h>
  56#include <linux/idr.h>
  57#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
  58#include <linux/kthread.h>
  59#include <linux/delay.h>
  60#include <linux/atomic.h>
  61#include <linux/cpuset.h>
  62#include <linux/proc_ns.h>
  63#include <linux/nsproxy.h>
  64#include <linux/file.h>
  65#include <net/sock.h>
  66
  67#define CREATE_TRACE_POINTS
  68#include <trace/events/cgroup.h>
  69
  70/*
  71 * pidlists linger the following amount before being destroyed.  The goal
  72 * is avoiding frequent destruction in the middle of consecutive read calls
  73 * Expiring in the middle is a performance problem not a correctness one.
  74 * 1 sec should be enough.
  75 */
  76#define CGROUP_PIDLIST_DESTROY_DELAY    HZ
  77
  78#define CGROUP_FILE_NAME_MAX            (MAX_CGROUP_TYPE_NAMELEN +      \
  79                                         MAX_CFTYPE_NAME + 2)
  80
  81/*
  82 * cgroup_mutex is the master lock.  Any modification to cgroup or its
  83 * hierarchy must be performed while holding it.
  84 *
  85 * css_set_lock protects task->cgroups pointer, the list of css_set
  86 * objects, and the chain of tasks off each css_set.
  87 *
  88 * These locks are exported if CONFIG_PROVE_RCU so that accessors in
  89 * cgroup.h can use them for lockdep annotations.
  90 */
  91#ifdef CONFIG_PROVE_RCU
  92DEFINE_MUTEX(cgroup_mutex);
  93DEFINE_SPINLOCK(css_set_lock);
  94EXPORT_SYMBOL_GPL(cgroup_mutex);
  95EXPORT_SYMBOL_GPL(css_set_lock);
  96#else
  97static DEFINE_MUTEX(cgroup_mutex);
  98static DEFINE_SPINLOCK(css_set_lock);
  99#endif
 100
 101/*
 102 * Protects cgroup_idr and css_idr so that IDs can be released without
 103 * grabbing cgroup_mutex.
 104 */
 105static DEFINE_SPINLOCK(cgroup_idr_lock);
 106
 107/*
 108 * Protects cgroup_file->kn for !self csses.  It synchronizes notifications
 109 * against file removal/re-creation across css hiding.
 110 */
 111static DEFINE_SPINLOCK(cgroup_file_kn_lock);
 112
 113/*
 114 * Protects cgroup_subsys->release_agent_path.  Modifying it also requires
 115 * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.
 116 */
 117static DEFINE_SPINLOCK(release_agent_path_lock);
 118
 119struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
 120
 121#define cgroup_assert_mutex_or_rcu_locked()                             \
 122        RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
 123                           !lockdep_is_held(&cgroup_mutex),             \
 124                           "cgroup_mutex or RCU read lock required");
 125
 126/*
 127 * cgroup destruction makes heavy use of work items and there can be a lot
 128 * of concurrent destructions.  Use a separate workqueue so that cgroup
 129 * destruction work items don't end up filling up max_active of system_wq
 130 * which may lead to deadlock.
 131 */
 132static struct workqueue_struct *cgroup_destroy_wq;
 133
 134/*
 135 * pidlist destructions need to be flushed on cgroup destruction.  Use a
 136 * separate workqueue as flush domain.
 137 */
 138static struct workqueue_struct *cgroup_pidlist_destroy_wq;
 139
 140/* generate an array of cgroup subsystem pointers */
 141#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys,
 142static struct cgroup_subsys *cgroup_subsys[] = {
 143#include <linux/cgroup_subsys.h>
 144};
 145#undef SUBSYS
 146
 147/* array of cgroup subsystem names */
 148#define SUBSYS(_x) [_x ## _cgrp_id] = #_x,
 149static const char *cgroup_subsys_name[] = {
 150#include <linux/cgroup_subsys.h>
 151};
 152#undef SUBSYS
 153
 154/* array of static_keys for cgroup_subsys_enabled() and cgroup_subsys_on_dfl() */
 155#define SUBSYS(_x)                                                              \
 156        DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_enabled_key);                 \
 157        DEFINE_STATIC_KEY_TRUE(_x ## _cgrp_subsys_on_dfl_key);                  \
 158        EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_enabled_key);                      \
 159        EXPORT_SYMBOL_GPL(_x ## _cgrp_subsys_on_dfl_key);
 160#include <linux/cgroup_subsys.h>
 161#undef SUBSYS
 162
 163#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_enabled_key,
 164static struct static_key_true *cgroup_subsys_enabled_key[] = {
 165#include <linux/cgroup_subsys.h>
 166};
 167#undef SUBSYS
 168
 169#define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys_on_dfl_key,
 170static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
 171#include <linux/cgroup_subsys.h>
 172};
 173#undef SUBSYS
 174
 175/*
 176 * The default hierarchy, reserved for the subsystems that are otherwise
 177 * unattached - it never has more than a single cgroup, and all tasks are
 178 * part of that cgroup.
 179 */
 180struct cgroup_root cgrp_dfl_root;
 181EXPORT_SYMBOL_GPL(cgrp_dfl_root);
 182
 183/*
 184 * The default hierarchy always exists but is hidden until mounted for the
 185 * first time.  This is for backward compatibility.
 186 */
 187static bool cgrp_dfl_visible;
 188
 189/* Controllers blocked by the commandline in v1 */
 190static u16 cgroup_no_v1_mask;
 191
 192/* some controllers are not supported in the default hierarchy */
 193static u16 cgrp_dfl_inhibit_ss_mask;
 194
 195/* some controllers are implicitly enabled on the default hierarchy */
 196static unsigned long cgrp_dfl_implicit_ss_mask;
 197
 198/* The list of hierarchy roots */
 199
 200static LIST_HEAD(cgroup_roots);
 201static int cgroup_root_count;
 202
 203/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
 204static DEFINE_IDR(cgroup_hierarchy_idr);
 205
 206/*
 207 * Assign a monotonically increasing serial number to csses.  It guarantees
 208 * cgroups with bigger numbers are newer than those with smaller numbers.
 209 * Also, as csses are always appended to the parent's ->children list, it
 210 * guarantees that sibling csses are always sorted in the ascending serial
 211 * number order on the list.  Protected by cgroup_mutex.
 212 */
 213static u64 css_serial_nr_next = 1;
 214
 215/*
 216 * These bitmask flags indicate whether tasks in the fork and exit paths have
 217 * fork/exit handlers to call. This avoids us having to do extra work in the
 218 * fork/exit path to check which subsystems have fork/exit callbacks.
 219 */
 220static u16 have_fork_callback __read_mostly;
 221static u16 have_exit_callback __read_mostly;
 222static u16 have_free_callback __read_mostly;
 223
 224/* cgroup namespace for init task */
 225struct cgroup_namespace init_cgroup_ns = {
 226        .count          = { .counter = 2, },
 227        .user_ns        = &init_user_ns,
 228        .ns.ops         = &cgroupns_operations,
 229        .ns.inum        = PROC_CGROUP_INIT_INO,
 230        .root_cset      = &init_css_set,
 231};
 232
 233/* Ditto for the can_fork callback. */
 234static u16 have_canfork_callback __read_mostly;
 235
 236static struct file_system_type cgroup2_fs_type;
 237static struct cftype cgroup_dfl_base_files[];
 238static struct cftype cgroup_legacy_base_files[];
 239
 240static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
 241static void cgroup_lock_and_drain_offline(struct cgroup *cgrp);
 242static int cgroup_apply_control(struct cgroup *cgrp);
 243static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
 244static void css_task_iter_advance(struct css_task_iter *it);
 245static int cgroup_destroy_locked(struct cgroup *cgrp);
 246static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 247                                              struct cgroup_subsys *ss);
 248static void css_release(struct percpu_ref *ref);
 249static void kill_css(struct cgroup_subsys_state *css);
 250static int cgroup_addrm_files(struct cgroup_subsys_state *css,
 251                              struct cgroup *cgrp, struct cftype cfts[],
 252                              bool is_add);
 253
 254/**
 255 * cgroup_ssid_enabled - cgroup subsys enabled test by subsys ID
 256 * @ssid: subsys ID of interest
 257 *
 258 * cgroup_subsys_enabled() can only be used with literal subsys names which
 259 * is fine for individual subsystems but unsuitable for cgroup core.  This
 260 * is slower static_key_enabled() based test indexed by @ssid.
 261 */
 262static bool cgroup_ssid_enabled(int ssid)
 263{
 264        if (CGROUP_SUBSYS_COUNT == 0)
 265                return false;
 266
 267        return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
 268}
 269
 270static bool cgroup_ssid_no_v1(int ssid)
 271{
 272        return cgroup_no_v1_mask & (1 << ssid);
 273}
 274
 275/**
 276 * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
 277 * @cgrp: the cgroup of interest
 278 *
 279 * The default hierarchy is the v2 interface of cgroup and this function
 280 * can be used to test whether a cgroup is on the default hierarchy for
 281 * cases where a subsystem should behave differnetly depending on the
 282 * interface version.
 283 *
 284 * The set of behaviors which change on the default hierarchy are still
 285 * being determined and the mount option is prefixed with __DEVEL__.
 286 *
 287 * List of changed behaviors:
 288 *
 289 * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
 290 *   and "name" are disallowed.
 291 *
 292 * - When mounting an existing superblock, mount options should match.
 293 *
 294 * - Remount is disallowed.
 295 *
 296 * - rename(2) is disallowed.
 297 *
 298 * - "tasks" is removed.  Everything should be at process granularity.  Use
 299 *   "cgroup.procs" instead.
 300 *
 301 * - "cgroup.procs" is not sorted.  pids will be unique unless they got
 302 *   recycled inbetween reads.
 303 *
 304 * - "release_agent" and "notify_on_release" are removed.  Replacement
 305 *   notification mechanism will be implemented.
 306 *
 307 * - "cgroup.clone_children" is removed.
 308 *
 309 * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
 310 *   and its descendants contain no task; otherwise, 1.  The file also
 311 *   generates kernfs notification which can be monitored through poll and
 312 *   [di]notify when the value of the file changes.
 313 *
 314 * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
 315 *   take masks of ancestors with non-empty cpus/mems, instead of being
 316 *   moved to an ancestor.
 317 *
 318 * - cpuset: a task can be moved into an empty cpuset, and again it takes
 319 *   masks of ancestors.
 320 *
 321 * - memcg: use_hierarchy is on by default and the cgroup file for the flag
 322 *   is not created.
 323 *
 324 * - blkcg: blk-throttle becomes properly hierarchical.
 325 *
 326 * - debug: disallowed on the default hierarchy.
 327 */
 328static bool cgroup_on_dfl(const struct cgroup *cgrp)
 329{
 330        return cgrp->root == &cgrp_dfl_root;
 331}
 332
 333/* IDR wrappers which synchronize using cgroup_idr_lock */
 334static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
 335                            gfp_t gfp_mask)
 336{
 337        int ret;
 338
 339        idr_preload(gfp_mask);
 340        spin_lock_bh(&cgroup_idr_lock);
 341        ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_DIRECT_RECLAIM);
 342        spin_unlock_bh(&cgroup_idr_lock);
 343        idr_preload_end();
 344        return ret;
 345}
 346
 347static void *cgroup_idr_replace(struct idr *idr, void *ptr, int id)
 348{
 349        void *ret;
 350
 351        spin_lock_bh(&cgroup_idr_lock);
 352        ret = idr_replace(idr, ptr, id);
 353        spin_unlock_bh(&cgroup_idr_lock);
 354        return ret;
 355}
 356
 357static void cgroup_idr_remove(struct idr *idr, int id)
 358{
 359        spin_lock_bh(&cgroup_idr_lock);
 360        idr_remove(idr, id);
 361        spin_unlock_bh(&cgroup_idr_lock);
 362}
 363
 364static struct cgroup *cgroup_parent(struct cgroup *cgrp)
 365{
 366        struct cgroup_subsys_state *parent_css = cgrp->self.parent;
 367
 368        if (parent_css)
 369                return container_of(parent_css, struct cgroup, self);
 370        return NULL;
 371}
 372
 373/* subsystems visibly enabled on a cgroup */
 374static u16 cgroup_control(struct cgroup *cgrp)
 375{
 376        struct cgroup *parent = cgroup_parent(cgrp);
 377        u16 root_ss_mask = cgrp->root->subsys_mask;
 378
 379        if (parent)
 380                return parent->subtree_control;
 381
 382        if (cgroup_on_dfl(cgrp))
 383                root_ss_mask &= ~(cgrp_dfl_inhibit_ss_mask |
 384                                  cgrp_dfl_implicit_ss_mask);
 385        return root_ss_mask;
 386}
 387
 388/* subsystems enabled on a cgroup */
 389static u16 cgroup_ss_mask(struct cgroup *cgrp)
 390{
 391        struct cgroup *parent = cgroup_parent(cgrp);
 392
 393        if (parent)
 394                return parent->subtree_ss_mask;
 395
 396        return cgrp->root->subsys_mask;
 397}
 398
 399/**
 400 * cgroup_css - obtain a cgroup's css for the specified subsystem
 401 * @cgrp: the cgroup of interest
 402 * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 403 *
 404 * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This
 405 * function must be called either under cgroup_mutex or rcu_read_lock() and
 406 * the caller is responsible for pinning the returned css if it wants to
 407 * keep accessing it outside the said locks.  This function may return
 408 * %NULL if @cgrp doesn't have @subsys_id enabled.
 409 */
 410static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
 411                                              struct cgroup_subsys *ss)
 412{
 413        if (ss)
 414                return rcu_dereference_check(cgrp->subsys[ss->id],
 415                                        lockdep_is_held(&cgroup_mutex));
 416        else
 417                return &cgrp->self;
 418}
 419
 420/**
 421 * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
 422 * @cgrp: the cgroup of interest
 423 * @ss: the subsystem of interest (%NULL returns @cgrp->self)
 424 *
 425 * Similar to cgroup_css() but returns the effective css, which is defined
 426 * as the matching css of the nearest ancestor including self which has @ss
 427 * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
 428 * function is guaranteed to return non-NULL css.
 429 */
 430static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
 431                                                struct cgroup_subsys *ss)
 432{
 433        lockdep_assert_held(&cgroup_mutex);
 434
 435        if (!ss)
 436                return &cgrp->self;
 437
 438        /*
 439         * This function is used while updating css associations and thus
 440         * can't test the csses directly.  Test ss_mask.
 441         */
 442        while (!(cgroup_ss_mask(cgrp) & (1 << ss->id))) {
 443                cgrp = cgroup_parent(cgrp);
 444                if (!cgrp)
 445                        return NULL;
 446        }
 447
 448        return cgroup_css(cgrp, ss);
 449}
 450
 451/**
 452 * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
 453 * @cgrp: the cgroup of interest
 454 * @ss: the subsystem of interest
 455 *
 456 * Find and get the effective css of @cgrp for @ss.  The effective css is
 457 * defined as the matching css of the nearest ancestor including self which
 458 * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
 459 * the root css is returned, so this function always returns a valid css.
 460 * The returned css must be put using css_put().
 461 */
 462struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
 463                                             struct cgroup_subsys *ss)
 464{
 465        struct cgroup_subsys_state *css;
 466
 467        rcu_read_lock();
 468
 469        do {
 470                css = cgroup_css(cgrp, ss);
 471
 472                if (css && css_tryget_online(css))
 473                        goto out_unlock;
 474                cgrp = cgroup_parent(cgrp);
 475        } while (cgrp);
 476
 477        css = init_css_set.subsys[ss->id];
 478        css_get(css);
 479out_unlock:
 480        rcu_read_unlock();
 481        return css;
 482}
 483
 484/* convenient tests for these bits */
 485static inline bool cgroup_is_dead(const struct cgroup *cgrp)
 486{
 487        return !(cgrp->self.flags & CSS_ONLINE);
 488}
 489
 490static void cgroup_get(struct cgroup *cgrp)
 491{
 492        WARN_ON_ONCE(cgroup_is_dead(cgrp));
 493        css_get(&cgrp->self);
 494}
 495
 496static bool cgroup_tryget(struct cgroup *cgrp)
 497{
 498        return css_tryget(&cgrp->self);
 499}
 500
 501struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
 502{
 503        struct cgroup *cgrp = of->kn->parent->priv;
 504        struct cftype *cft = of_cft(of);
 505
 506        /*
 507         * This is open and unprotected implementation of cgroup_css().
 508         * seq_css() is only called from a kernfs file operation which has
 509         * an active reference on the file.  Because all the subsystem
 510         * files are drained before a css is disassociated with a cgroup,
 511         * the matching css from the cgroup's subsys table is guaranteed to
 512         * be and stay valid until the enclosing operation is complete.
 513         */
 514        if (cft->ss)
 515                return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
 516        else
 517                return &cgrp->self;
 518}
 519EXPORT_SYMBOL_GPL(of_css);
 520
 521static int notify_on_release(const struct cgroup *cgrp)
 522{
 523        return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
 524}
 525
 526/**
 527 * for_each_css - iterate all css's of a cgroup
 528 * @css: the iteration cursor
 529 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 530 * @cgrp: the target cgroup to iterate css's of
 531 *
 532 * Should be called under cgroup_[tree_]mutex.
 533 */
 534#define for_each_css(css, ssid, cgrp)                                   \
 535        for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
 536                if (!((css) = rcu_dereference_check(                    \
 537                                (cgrp)->subsys[(ssid)],                 \
 538                                lockdep_is_held(&cgroup_mutex)))) { }   \
 539                else
 540
 541/**
 542 * for_each_e_css - iterate all effective css's of a cgroup
 543 * @css: the iteration cursor
 544 * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end
 545 * @cgrp: the target cgroup to iterate css's of
 546 *
 547 * Should be called under cgroup_[tree_]mutex.
 548 */
 549#define for_each_e_css(css, ssid, cgrp)                                 \
 550        for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)        \
 551                if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
 552                        ;                                               \
 553                else
 554
 555/**
 556 * for_each_subsys - iterate all enabled cgroup subsystems
 557 * @ss: the iteration cursor
 558 * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
 559 */
 560#define for_each_subsys(ss, ssid)                                       \
 561        for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT &&                \
 562             (((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
 563
 564/**
 565 * do_each_subsys_mask - filter for_each_subsys with a bitmask
 566 * @ss: the iteration cursor
 567 * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
 568 * @ss_mask: the bitmask
 569 *
 570 * The block will only run for cases where the ssid-th bit (1 << ssid) of
 571 * @ss_mask is set.
 572 */
 573#define do_each_subsys_mask(ss, ssid, ss_mask) do {                     \
 574        unsigned long __ss_mask = (ss_mask);                            \
 575        if (!CGROUP_SUBSYS_COUNT) { /* to avoid spurious gcc warning */ \
 576                (ssid) = 0;                                             \
 577                break;                                                  \
 578        }                                                               \
 579        for_each_set_bit(ssid, &__ss_mask, CGROUP_SUBSYS_COUNT) {       \
 580                (ss) = cgroup_subsys[ssid];                             \
 581                {
 582
 583#define while_each_subsys_mask()                                        \
 584                }                                                       \
 585        }                                                               \
 586} while (false)
 587
 588/* iterate across the hierarchies */
 589#define for_each_root(root)                                             \
 590        list_for_each_entry((root), &cgroup_roots, root_list)
 591
 592/* iterate over child cgrps, lock should be held throughout iteration */
 593#define cgroup_for_each_live_child(child, cgrp)                         \
 594        list_for_each_entry((child), &(cgrp)->self.children, self.sibling) \
 595                if (({ lockdep_assert_held(&cgroup_mutex);              \
 596                       cgroup_is_dead(child); }))                       \
 597                        ;                                               \
 598                else
 599
 600/* walk live descendants in preorder */
 601#define cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)          \
 602        css_for_each_descendant_pre((d_css), cgroup_css((cgrp), NULL))  \
 603                if (({ lockdep_assert_held(&cgroup_mutex);              \
 604                       (dsct) = (d_css)->cgroup;                        \
 605                       cgroup_is_dead(dsct); }))                        \
 606                        ;                                               \
 607                else
 608
 609/* walk live descendants in postorder */
 610#define cgroup_for_each_live_descendant_post(dsct, d_css, cgrp)         \
 611        css_for_each_descendant_post((d_css), cgroup_css((cgrp), NULL)) \
 612                if (({ lockdep_assert_held(&cgroup_mutex);              \
 613                       (dsct) = (d_css)->cgroup;                        \
 614                       cgroup_is_dead(dsct); }))                        \
 615                        ;                                               \
 616                else
 617
 618static void cgroup_release_agent(struct work_struct *work);
 619static void check_for_release(struct cgroup *cgrp);
 620
 621/*
 622 * A cgroup can be associated with multiple css_sets as different tasks may
 623 * belong to different cgroups on different hierarchies.  In the other
 624 * direction, a css_set is naturally associated with multiple cgroups.
 625 * This M:N relationship is represented by the following link structure
 626 * which exists for each association and allows traversing the associations
 627 * from both sides.
 628 */
 629struct cgrp_cset_link {
 630        /* the cgroup and css_set this link associates */
 631        struct cgroup           *cgrp;
 632        struct css_set          *cset;
 633
 634        /* list of cgrp_cset_links anchored at cgrp->cset_links */
 635        struct list_head        cset_link;
 636
 637        /* list of cgrp_cset_links anchored at css_set->cgrp_links */
 638        struct list_head        cgrp_link;
 639};
 640
 641/*
 642 * The default css_set - used by init and its children prior to any
 643 * hierarchies being mounted. It contains a pointer to the root state
 644 * for each subsystem. Also used to anchor the list of css_sets. Not
 645 * reference-counted, to improve performance when child cgroups
 646 * haven't been created.
 647 */
 648struct css_set init_css_set = {
 649        .refcount               = ATOMIC_INIT(1),
 650        .cgrp_links             = LIST_HEAD_INIT(init_css_set.cgrp_links),
 651        .tasks                  = LIST_HEAD_INIT(init_css_set.tasks),
 652        .mg_tasks               = LIST_HEAD_INIT(init_css_set.mg_tasks),
 653        .mg_preload_node        = LIST_HEAD_INIT(init_css_set.mg_preload_node),
 654        .mg_node                = LIST_HEAD_INIT(init_css_set.mg_node),
 655        .task_iters             = LIST_HEAD_INIT(init_css_set.task_iters),
 656};
 657
 658static int css_set_count        = 1;    /* 1 for init_css_set */
 659
 660/**
 661 * css_set_populated - does a css_set contain any tasks?
 662 * @cset: target css_set
 663 */
 664static bool css_set_populated(struct css_set *cset)
 665{
 666        lockdep_assert_held(&css_set_lock);
 667
 668        return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
 669}
 670
 671/**
 672 * cgroup_update_populated - updated populated count of a cgroup
 673 * @cgrp: the target cgroup
 674 * @populated: inc or dec populated count
 675 *
 676 * One of the css_sets associated with @cgrp is either getting its first
 677 * task or losing the last.  Update @cgrp->populated_cnt accordingly.  The
 678 * count is propagated towards root so that a given cgroup's populated_cnt
 679 * is zero iff the cgroup and all its descendants don't contain any tasks.
 680 *
 681 * @cgrp's interface file "cgroup.populated" is zero if
 682 * @cgrp->populated_cnt is zero and 1 otherwise.  When @cgrp->populated_cnt
 683 * changes from or to zero, userland is notified that the content of the
 684 * interface file has changed.  This can be used to detect when @cgrp and
 685 * its descendants become populated or empty.
 686 */
 687static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
 688{
 689        lockdep_assert_held(&css_set_lock);
 690
 691        do {
 692                bool trigger;
 693
 694                if (populated)
 695                        trigger = !cgrp->populated_cnt++;
 696                else
 697                        trigger = !--cgrp->populated_cnt;
 698
 699                if (!trigger)
 700                        break;
 701
 702                check_for_release(cgrp);
 703                cgroup_file_notify(&cgrp->events_file);
 704
 705                cgrp = cgroup_parent(cgrp);
 706        } while (cgrp);
 707}
 708
 709/**
 710 * css_set_update_populated - update populated state of a css_set
 711 * @cset: target css_set
 712 * @populated: whether @cset is populated or depopulated
 713 *
 714 * @cset is either getting the first task or losing the last.  Update the
 715 * ->populated_cnt of all associated cgroups accordingly.
 716 */
 717static void css_set_update_populated(struct css_set *cset, bool populated)
 718{
 719        struct cgrp_cset_link *link;
 720
 721        lockdep_assert_held(&css_set_lock);
 722
 723        list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
 724                cgroup_update_populated(link->cgrp, populated);
 725}
 726
 727/**
 728 * css_set_move_task - move a task from one css_set to another
 729 * @task: task being moved
 730 * @from_cset: css_set @task currently belongs to (may be NULL)
 731 * @to_cset: new css_set @task is being moved to (may be NULL)
 732 * @use_mg_tasks: move to @to_cset->mg_tasks instead of ->tasks
 733 *
 734 * Move @task from @from_cset to @to_cset.  If @task didn't belong to any
 735 * css_set, @from_cset can be NULL.  If @task is being disassociated
 736 * instead of moved, @to_cset can be NULL.
 737 *
 738 * This function automatically handles populated_cnt updates and
 739 * css_task_iter adjustments but the caller is responsible for managing
 740 * @from_cset and @to_cset's reference counts.
 741 */
 742static void css_set_move_task(struct task_struct *task,
 743                              struct css_set *from_cset, struct css_set *to_cset,
 744                              bool use_mg_tasks)
 745{
 746        lockdep_assert_held(&css_set_lock);
 747
 748        if (to_cset && !css_set_populated(to_cset))
 749                css_set_update_populated(to_cset, true);
 750
 751        if (from_cset) {
 752                struct css_task_iter *it, *pos;
 753
 754                WARN_ON_ONCE(list_empty(&task->cg_list));
 755
 756                /*
 757                 * @task is leaving, advance task iterators which are
 758                 * pointing to it so that they can resume at the next
 759                 * position.  Advancing an iterator might remove it from
 760                 * the list, use safe walk.  See css_task_iter_advance*()
 761                 * for details.
 762                 */
 763                list_for_each_entry_safe(it, pos, &from_cset->task_iters,
 764                                         iters_node)
 765                        if (it->task_pos == &task->cg_list)
 766                                css_task_iter_advance(it);
 767
 768                list_del_init(&task->cg_list);
 769                if (!css_set_populated(from_cset))
 770                        css_set_update_populated(from_cset, false);
 771        } else {
 772                WARN_ON_ONCE(!list_empty(&task->cg_list));
 773        }
 774
 775        if (to_cset) {
 776                /*
 777                 * We are synchronized through cgroup_threadgroup_rwsem
 778                 * against PF_EXITING setting such that we can't race
 779                 * against cgroup_exit() changing the css_set to
 780                 * init_css_set and dropping the old one.
 781                 */
 782                WARN_ON_ONCE(task->flags & PF_EXITING);
 783
 784                rcu_assign_pointer(task->cgroups, to_cset);
 785                list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
 786                                                             &to_cset->tasks);
 787        }
 788}
 789
 790/*
 791 * hash table for cgroup groups. This improves the performance to find
 792 * an existing css_set. This hash doesn't (currently) take into
 793 * account cgroups in empty hierarchies.
 794 */
 795#define CSS_SET_HASH_BITS       7
 796static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS);
 797
 798static unsigned long css_set_hash(struct cgroup_subsys_state *css[])
 799{
 800        unsigned long key = 0UL;
 801        struct cgroup_subsys *ss;
 802        int i;
 803
 804        for_each_subsys(ss, i)
 805                key += (unsigned long)css[i];
 806        key = (key >> 16) ^ key;
 807
 808        return key;
 809}
 810
 811static void put_css_set_locked(struct css_set *cset)
 812{
 813        struct cgrp_cset_link *link, *tmp_link;
 814        struct cgroup_subsys *ss;
 815        int ssid;
 816
 817        lockdep_assert_held(&css_set_lock);
 818
 819        if (!atomic_dec_and_test(&cset->refcount))
 820                return;
 821
 822        /* This css_set is dead. unlink it and release cgroup and css refs */
 823        for_each_subsys(ss, ssid) {
 824                list_del(&cset->e_cset_node[ssid]);
 825                css_put(cset->subsys[ssid]);
 826        }
 827        hash_del(&cset->hlist);
 828        css_set_count--;
 829
 830        list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) {
 831                list_del(&link->cset_link);
 832                list_del(&link->cgrp_link);
 833                if (cgroup_parent(link->cgrp))
 834                        cgroup_put(link->cgrp);
 835                kfree(link);
 836        }
 837
 838        kfree_rcu(cset, rcu_head);
 839}
 840
 841static void put_css_set(struct css_set *cset)
 842{
 843        unsigned long flags;
 844
 845        /*
 846         * Ensure that the refcount doesn't hit zero while any readers
 847         * can see it. Similar to atomic_dec_and_lock(), but for an
 848         * rwlock
 849         */
 850        if (atomic_add_unless(&cset->refcount, -1, 1))
 851                return;
 852
 853        spin_lock_irqsave(&css_set_lock, flags);
 854        put_css_set_locked(cset);
 855        spin_unlock_irqrestore(&css_set_lock, flags);
 856}
 857
 858/*
 859 * refcounted get/put for css_set objects
 860 */
 861static inline void get_css_set(struct css_set *cset)
 862{
 863        atomic_inc(&cset->refcount);
 864}
 865
 866/**
 867 * compare_css_sets - helper function for find_existing_css_set().
 868 * @cset: candidate css_set being tested
 869 * @old_cset: existing css_set for a task
 870 * @new_cgrp: cgroup that's being entered by the task
 871 * @template: desired set of css pointers in css_set (pre-calculated)
 872 *
 873 * Returns true if "cset" matches "old_cset" except for the hierarchy
 874 * which "new_cgrp" belongs to, for which it should match "new_cgrp".
 875 */
 876static bool compare_css_sets(struct css_set *cset,
 877                             struct css_set *old_cset,
 878                             struct cgroup *new_cgrp,
 879                             struct cgroup_subsys_state *template[])
 880{
 881        struct list_head *l1, *l2;
 882
 883        /*
 884         * On the default hierarchy, there can be csets which are
 885         * associated with the same set of cgroups but different csses.
 886         * Let's first ensure that csses match.
 887         */
 888        if (memcmp(template, cset->subsys, sizeof(cset->subsys)))
 889                return false;
 890
 891        /*
 892         * Compare cgroup pointers in order to distinguish between
 893         * different cgroups in hierarchies.  As different cgroups may
 894         * share the same effective css, this comparison is always
 895         * necessary.
 896         */
 897        l1 = &cset->cgrp_links;
 898        l2 = &old_cset->cgrp_links;
 899        while (1) {
 900                struct cgrp_cset_link *link1, *link2;
 901                struct cgroup *cgrp1, *cgrp2;
 902
 903                l1 = l1->next;
 904                l2 = l2->next;
 905                /* See if we reached the end - both lists are equal length. */
 906                if (l1 == &cset->cgrp_links) {
 907                        BUG_ON(l2 != &old_cset->cgrp_links);
 908                        break;
 909                } else {
 910                        BUG_ON(l2 == &old_cset->cgrp_links);
 911                }
 912                /* Locate the cgroups associated with these links. */
 913                link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link);
 914                link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link);
 915                cgrp1 = link1->cgrp;
 916                cgrp2 = link2->cgrp;
 917                /* Hierarchies should be linked in the same order. */
 918                BUG_ON(cgrp1->root != cgrp2->root);
 919
 920                /*
 921                 * If this hierarchy is the hierarchy of the cgroup
 922                 * that's changing, then we need to check that this
 923                 * css_set points to the new cgroup; if it's any other
 924                 * hierarchy, then this css_set should point to the
 925                 * same cgroup as the old css_set.
 926                 */
 927                if (cgrp1->root == new_cgrp->root) {
 928                        if (cgrp1 != new_cgrp)
 929                                return false;
 930                } else {
 931                        if (cgrp1 != cgrp2)
 932                                return false;
 933                }
 934        }
 935        return true;
 936}
 937
 938/**
 939 * find_existing_css_set - init css array and find the matching css_set
 940 * @old_cset: the css_set that we're using before the cgroup transition
 941 * @cgrp: the cgroup that we're moving into
 942 * @template: out param for the new set of csses, should be clear on entry
 943 */
 944static struct css_set *find_existing_css_set(struct css_set *old_cset,
 945                                        struct cgroup *cgrp,
 946                                        struct cgroup_subsys_state *template[])
 947{
 948        struct cgroup_root *root = cgrp->root;
 949        struct cgroup_subsys *ss;
 950        struct css_set *cset;
 951        unsigned long key;
 952        int i;
 953
 954        /*
 955         * Build the set of subsystem state objects that we want to see in the
 956         * new css_set. while subsystems can change globally, the entries here
 957         * won't change, so no need for locking.
 958         */
 959        for_each_subsys(ss, i) {
 960                if (root->subsys_mask & (1UL << i)) {
 961                        /*
 962                         * @ss is in this hierarchy, so we want the
 963                         * effective css from @cgrp.
 964                         */
 965                        template[i] = cgroup_e_css(cgrp, ss);
 966                } else {
 967                        /*
 968                         * @ss is not in this hierarchy, so we don't want
 969                         * to change the css.
 970                         */
 971                        template[i] = old_cset->subsys[i];
 972                }
 973        }
 974
 975        key = css_set_hash(template);
 976        hash_for_each_possible(css_set_table, cset, hlist, key) {
 977                if (!compare_css_sets(cset, old_cset, cgrp, template))
 978                        continue;
 979
 980                /* This css_set matches what we need */
 981                return cset;
 982        }
 983
 984        /* No existing cgroup group matched */
 985        return NULL;
 986}
 987
 988static void free_cgrp_cset_links(struct list_head *links_to_free)
 989{
 990        struct cgrp_cset_link *link, *tmp_link;
 991
 992        list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) {
 993                list_del(&link->cset_link);
 994                kfree(link);
 995        }
 996}
 997
 998/**
 999 * allocate_cgrp_cset_links - allocate cgrp_cset_links
1000 * @count: the number of links to allocate
1001 * @tmp_links: list_head the allocated links are put on
1002 *
1003 * Allocate @count cgrp_cset_link structures and chain them on @tmp_links
1004 * through ->cset_link.  Returns 0 on success or -errno.
1005 */
1006static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links)
1007{
1008        struct cgrp_cset_link *link;
1009        int i;
1010
1011        INIT_LIST_HEAD(tmp_links);
1012
1013        for (i = 0; i < count; i++) {
1014                link = kzalloc(sizeof(*link), GFP_KERNEL);
1015                if (!link) {
1016                        free_cgrp_cset_links(tmp_links);
1017                        return -ENOMEM;
1018                }
1019                list_add(&link->cset_link, tmp_links);
1020        }
1021        return 0;
1022}
1023
1024/**
1025 * link_css_set - a helper function to link a css_set to a cgroup
1026 * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links()
1027 * @cset: the css_set to be linked
1028 * @cgrp: the destination cgroup
1029 */
1030static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
1031                         struct cgroup *cgrp)
1032{
1033        struct cgrp_cset_link *link;
1034
1035        BUG_ON(list_empty(tmp_links));
1036
1037        if (cgroup_on_dfl(cgrp))
1038                cset->dfl_cgrp = cgrp;
1039
1040        link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);
1041        link->cset = cset;
1042        link->cgrp = cgrp;
1043
1044        /*
1045         * Always add links to the tail of the lists so that the lists are
1046         * in choronological order.
1047         */
1048        list_move_tail(&link->cset_link, &cgrp->cset_links);
1049        list_add_tail(&link->cgrp_link, &cset->cgrp_links);
1050
1051        if (cgroup_parent(cgrp))
1052                cgroup_get(cgrp);
1053}
1054
1055/**
1056 * find_css_set - return a new css_set with one cgroup updated
1057 * @old_cset: the baseline css_set
1058 * @cgrp: the cgroup to be updated
1059 *
1060 * Return a new css_set that's equivalent to @old_cset, but with @cgrp
1061 * substituted into the appropriate hierarchy.
1062 */
1063static struct css_set *find_css_set(struct css_set *old_cset,
1064                                    struct cgroup *cgrp)
1065{
1066        struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { };
1067        struct css_set *cset;
1068        struct list_head tmp_links;
1069        struct cgrp_cset_link *link;
1070        struct cgroup_subsys *ss;
1071        unsigned long key;
1072        int ssid;
1073
1074        lockdep_assert_held(&cgroup_mutex);
1075
1076        /* First see if we already have a cgroup group that matches
1077         * the desired set */
1078        spin_lock_irq(&css_set_lock);
1079        cset = find_existing_css_set(old_cset, cgrp, template);
1080        if (cset)
1081                get_css_set(cset);
1082        spin_unlock_irq(&css_set_lock);
1083
1084        if (cset)
1085                return cset;
1086
1087        cset = kzalloc(sizeof(*cset), GFP_KERNEL);
1088        if (!cset)
1089                return NULL;
1090
1091        /* Allocate all the cgrp_cset_link objects that we'll need */
1092        if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) {
1093                kfree(cset);
1094                return NULL;
1095        }
1096
1097        atomic_set(&cset->refcount, 1);
1098        INIT_LIST_HEAD(&cset->cgrp_links);
1099        INIT_LIST_HEAD(&cset->tasks);
1100        INIT_LIST_HEAD(&cset->mg_tasks);
1101        INIT_LIST_HEAD(&cset->mg_preload_node);
1102        INIT_LIST_HEAD(&cset->mg_node);
1103        INIT_LIST_HEAD(&cset->task_iters);
1104        INIT_HLIST_NODE(&cset->hlist);
1105
1106        /* Copy the set of subsystem state objects generated in
1107         * find_existing_css_set() */
1108        memcpy(cset->subsys, template, sizeof(cset->subsys));
1109
1110        spin_lock_irq(&css_set_lock);
1111        /* Add reference counts and links from the new css_set. */
1112        list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) {
1113                struct cgroup *c = link->cgrp;
1114
1115                if (c->root == cgrp->root)
1116                        c = cgrp;
1117                link_css_set(&tmp_links, cset, c);
1118        }
1119
1120        BUG_ON(!list_empty(&tmp_links));
1121
1122        css_set_count++;
1123
1124        /* Add @cset to the hash table */
1125        key = css_set_hash(cset->subsys);
1126        hash_add(css_set_table, &cset->hlist, key);
1127
1128        for_each_subsys(ss, ssid) {
1129                struct cgroup_subsys_state *css = cset->subsys[ssid];
1130
1131                list_add_tail(&cset->e_cset_node[ssid],
1132                              &css->cgroup->e_csets[ssid]);
1133                css_get(css);
1134        }
1135
1136        spin_unlock_irq(&css_set_lock);
1137
1138        return cset;
1139}
1140
1141static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
1142{
1143        struct cgroup *root_cgrp = kf_root->kn->priv;
1144
1145        return root_cgrp->root;
1146}
1147
1148static int cgroup_init_root_id(struct cgroup_root *root)
1149{
1150        int id;
1151
1152        lockdep_assert_held(&cgroup_mutex);
1153
1154        id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL);
1155        if (id < 0)
1156                return id;
1157
1158        root->hierarchy_id = id;
1159        return 0;
1160}
1161
1162static void cgroup_exit_root_id(struct cgroup_root *root)
1163{
1164        lockdep_assert_held(&cgroup_mutex);
1165
1166        idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
1167}
1168
1169static void cgroup_free_root(struct cgroup_root *root)
1170{
1171        if (root) {
1172                idr_destroy(&root->cgroup_idr);
1173                kfree(root);
1174        }
1175}
1176
1177static void cgroup_destroy_root(struct cgroup_root *root)
1178{
1179        struct cgroup *cgrp = &root->cgrp;
1180        struct cgrp_cset_link *link, *tmp_link;
1181
1182        trace_cgroup_destroy_root(root);
1183
1184        cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1185
1186        BUG_ON(atomic_read(&root->nr_cgrps));
1187        BUG_ON(!list_empty(&cgrp->self.children));
1188
1189        /* Rebind all subsystems back to the default hierarchy */
1190        WARN_ON(rebind_subsystems(&cgrp_dfl_root, root->subsys_mask));
1191
1192        /*
1193         * Release all the links from cset_links to this hierarchy's
1194         * root cgroup
1195         */
1196        spin_lock_irq(&css_set_lock);
1197
1198        list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) {
1199                list_del(&link->cset_link);
1200                list_del(&link->cgrp_link);
1201                kfree(link);
1202        }
1203
1204        spin_unlock_irq(&css_set_lock);
1205
1206        if (!list_empty(&root->root_list)) {
1207                list_del(&root->root_list);
1208                cgroup_root_count--;
1209        }
1210
1211        cgroup_exit_root_id(root);
1212
1213        mutex_unlock(&cgroup_mutex);
1214
1215        kernfs_destroy_root(root->kf_root);
1216        cgroup_free_root(root);
1217}
1218
1219/*
1220 * look up cgroup associated with current task's cgroup namespace on the
1221 * specified hierarchy
1222 */
1223static struct cgroup *
1224current_cgns_cgroup_from_root(struct cgroup_root *root)
1225{
1226        struct cgroup *res = NULL;
1227        struct css_set *cset;
1228
1229        lockdep_assert_held(&css_set_lock);
1230
1231        rcu_read_lock();
1232
1233        cset = current->nsproxy->cgroup_ns->root_cset;
1234        if (cset == &init_css_set) {
1235                res = &root->cgrp;
1236        } else {
1237                struct cgrp_cset_link *link;
1238
1239                list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1240                        struct cgroup *c = link->cgrp;
1241
1242                        if (c->root == root) {
1243                                res = c;
1244                                break;
1245                        }
1246                }
1247        }
1248        rcu_read_unlock();
1249
1250        BUG_ON(!res);
1251        return res;
1252}
1253
1254/* look up cgroup associated with given css_set on the specified hierarchy */
1255static struct cgroup *cset_cgroup_from_root(struct css_set *cset,
1256                                            struct cgroup_root *root)
1257{
1258        struct cgroup *res = NULL;
1259
1260        lockdep_assert_held(&cgroup_mutex);
1261        lockdep_assert_held(&css_set_lock);
1262
1263        if (cset == &init_css_set) {
1264                res = &root->cgrp;
1265        } else {
1266                struct cgrp_cset_link *link;
1267
1268                list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
1269                        struct cgroup *c = link->cgrp;
1270
1271                        if (c->root == root) {
1272                                res = c;
1273                                break;
1274                        }
1275                }
1276        }
1277
1278        BUG_ON(!res);
1279        return res;
1280}
1281
1282/*
1283 * Return the cgroup for "task" from the given hierarchy. Must be
1284 * called with cgroup_mutex and css_set_lock held.
1285 */
1286static struct cgroup *task_cgroup_from_root(struct task_struct *task,
1287                                            struct cgroup_root *root)
1288{
1289        /*
1290         * No need to lock the task - since we hold cgroup_mutex the
1291         * task can't change groups, so the only thing that can happen
1292         * is that it exits and its css is set back to init_css_set.
1293         */
1294        return cset_cgroup_from_root(task_css_set(task), root);
1295}
1296
1297/*
1298 * A task must hold cgroup_mutex to modify cgroups.
1299 *
1300 * Any task can increment and decrement the count field without lock.
1301 * So in general, code holding cgroup_mutex can't rely on the count
1302 * field not changing.  However, if the count goes to zero, then only
1303 * cgroup_attach_task() can increment it again.  Because a count of zero
1304 * means that no tasks are currently attached, therefore there is no
1305 * way a task attached to that cgroup can fork (the other way to
1306 * increment the count).  So code holding cgroup_mutex can safely
1307 * assume that if the count is zero, it will stay zero. Similarly, if
1308 * a task holds cgroup_mutex on a cgroup with zero count, it
1309 * knows that the cgroup won't be removed, as cgroup_rmdir()
1310 * needs that mutex.
1311 *
1312 * A cgroup can only be deleted if both its 'count' of using tasks
1313 * is zero, and its list of 'children' cgroups is empty.  Since all
1314 * tasks in the system use _some_ cgroup, and since there is always at
1315 * least one task in the system (init, pid == 1), therefore, root cgroup
1316 * always has either children cgroups and/or using tasks.  So we don't
1317 * need a special hack to ensure that root cgroup cannot be deleted.
1318 *
1319 * P.S.  One more locking exception.  RCU is used to guard the
1320 * update of a tasks cgroup pointer by cgroup_attach_task()
1321 */
1322
1323static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
1324static const struct file_operations proc_cgroupstats_operations;
1325
1326static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
1327                              char *buf)
1328{
1329        struct cgroup_subsys *ss = cft->ss;
1330
1331        if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
1332            !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
1333                snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
1334                         cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
1335                         cft->name);
1336        else
1337                strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
1338        return buf;
1339}
1340
1341/**
1342 * cgroup_file_mode - deduce file mode of a control file
1343 * @cft: the control file in question
1344 *
1345 * S_IRUGO for read, S_IWUSR for write.
1346 */
1347static umode_t cgroup_file_mode(const struct cftype *cft)
1348{
1349        umode_t mode = 0;
1350
1351        if (cft->read_u64 || cft->read_s64 || cft->seq_show)
1352                mode |= S_IRUGO;
1353
1354        if (cft->write_u64 || cft->write_s64 || cft->write) {
1355                if (cft->flags & CFTYPE_WORLD_WRITABLE)
1356                        mode |= S_IWUGO;
1357                else
1358                        mode |= S_IWUSR;
1359        }
1360
1361        return mode;
1362}
1363
1364/**
1365 * cgroup_calc_subtree_ss_mask - calculate subtree_ss_mask
1366 * @subtree_control: the new subtree_control mask to consider
1367 * @this_ss_mask: available subsystems
1368 *
1369 * On the default hierarchy, a subsystem may request other subsystems to be
1370 * enabled together through its ->depends_on mask.  In such cases, more
1371 * subsystems than specified in "cgroup.subtree_control" may be enabled.
1372 *
1373 * This function calculates which subsystems need to be enabled if
1374 * @subtree_control is to be applied while restricted to @this_ss_mask.
1375 */
1376static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
1377{
1378        u16 cur_ss_mask = subtree_control;
1379        struct cgroup_subsys *ss;
1380        int ssid;
1381
1382        lockdep_assert_held(&cgroup_mutex);
1383
1384        cur_ss_mask |= cgrp_dfl_implicit_ss_mask;
1385
1386        while (true) {
1387                u16 new_ss_mask = cur_ss_mask;
1388
1389                do_each_subsys_mask(ss, ssid, cur_ss_mask) {
1390                        new_ss_mask |= ss->depends_on;
1391                } while_each_subsys_mask();
1392
1393                /*
1394                 * Mask out subsystems which aren't available.  This can
1395                 * happen only if some depended-upon subsystems were bound
1396                 * to non-default hierarchies.
1397                 */
1398                new_ss_mask &= this_ss_mask;
1399
1400                if (new_ss_mask == cur_ss_mask)
1401                        break;
1402                cur_ss_mask = new_ss_mask;
1403        }
1404
1405        return cur_ss_mask;
1406}
1407
1408/**
1409 * cgroup_kn_unlock - unlocking helper for cgroup kernfs methods
1410 * @kn: the kernfs_node being serviced
1411 *
1412 * This helper undoes cgroup_kn_lock_live() and should be invoked before
1413 * the method finishes if locking succeeded.  Note that once this function
1414 * returns the cgroup returned by cgroup_kn_lock_live() may become
1415 * inaccessible any time.  If the caller intends to continue to access the
1416 * cgroup, it should pin it before invoking this function.
1417 */
1418static void cgroup_kn_unlock(struct kernfs_node *kn)
1419{
1420        struct cgroup *cgrp;
1421
1422        if (kernfs_type(kn) == KERNFS_DIR)
1423                cgrp = kn->priv;
1424        else
1425                cgrp = kn->parent->priv;
1426
1427        mutex_unlock(&cgroup_mutex);
1428
1429        kernfs_unbreak_active_protection(kn);
1430        cgroup_put(cgrp);
1431}
1432
1433/**
1434 * cgroup_kn_lock_live - locking helper for cgroup kernfs methods
1435 * @kn: the kernfs_node being serviced
1436 * @drain_offline: perform offline draining on the cgroup
1437 *
1438 * This helper is to be used by a cgroup kernfs method currently servicing
1439 * @kn.  It breaks the active protection, performs cgroup locking and
1440 * verifies that the associated cgroup is alive.  Returns the cgroup if
1441 * alive; otherwise, %NULL.  A successful return should be undone by a
1442 * matching cgroup_kn_unlock() invocation.  If @drain_offline is %true, the
1443 * cgroup is drained of offlining csses before return.
1444 *
1445 * Any cgroup kernfs method implementation which requires locking the
1446 * associated cgroup should use this helper.  It avoids nesting cgroup
1447 * locking under kernfs active protection and allows all kernfs operations
1448 * including self-removal.
1449 */
1450static struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn,
1451                                          bool drain_offline)
1452{
1453        struct cgroup *cgrp;
1454
1455        if (kernfs_type(kn) == KERNFS_DIR)
1456                cgrp = kn->priv;
1457        else
1458                cgrp = kn->parent->priv;
1459
1460        /*
1461         * We're gonna grab cgroup_mutex which nests outside kernfs
1462         * active_ref.  cgroup liveliness check alone provides enough
1463         * protection against removal.  Ensure @cgrp stays accessible and
1464         * break the active_ref protection.
1465         */
1466        if (!cgroup_tryget(cgrp))
1467                return NULL;
1468        kernfs_break_active_protection(kn);
1469
1470        if (drain_offline)
1471                cgroup_lock_and_drain_offline(cgrp);
1472        else
1473                mutex_lock(&cgroup_mutex);
1474
1475        if (!cgroup_is_dead(cgrp))
1476                return cgrp;
1477
1478        cgroup_kn_unlock(kn);
1479        return NULL;
1480}
1481
1482static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
1483{
1484        char name[CGROUP_FILE_NAME_MAX];
1485
1486        lockdep_assert_held(&cgroup_mutex);
1487
1488        if (cft->file_offset) {
1489                struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
1490                struct cgroup_file *cfile = (void *)css + cft->file_offset;
1491
1492                spin_lock_irq(&cgroup_file_kn_lock);
1493                cfile->kn = NULL;
1494                spin_unlock_irq(&cgroup_file_kn_lock);
1495        }
1496
1497        kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
1498}
1499
1500/**
1501 * css_clear_dir - remove subsys files in a cgroup directory
1502 * @css: taget css
1503 */
1504static void css_clear_dir(struct cgroup_subsys_state *css)
1505{
1506        struct cgroup *cgrp = css->cgroup;
1507        struct cftype *cfts;
1508
1509        if (!(css->flags & CSS_VISIBLE))
1510                return;
1511
1512        css->flags &= ~CSS_VISIBLE;
1513
1514        list_for_each_entry(cfts, &css->ss->cfts, node)
1515                cgroup_addrm_files(css, cgrp, cfts, false);
1516}
1517
1518/**
1519 * css_populate_dir - create subsys files in a cgroup directory
1520 * @css: target css
1521 *
1522 * On failure, no file is added.
1523 */
1524static int css_populate_dir(struct cgroup_subsys_state *css)
1525{
1526        struct cgroup *cgrp = css->cgroup;
1527        struct cftype *cfts, *failed_cfts;
1528        int ret;
1529
1530        if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
1531                return 0;
1532
1533        if (!css->ss) {
1534                if (cgroup_on_dfl(cgrp))
1535                        cfts = cgroup_dfl_base_files;
1536                else
1537                        cfts = cgroup_legacy_base_files;
1538
1539                return cgroup_addrm_files(&cgrp->self, cgrp, cfts, true);
1540        }
1541
1542        list_for_each_entry(cfts, &css->ss->cfts, node) {
1543                ret = cgroup_addrm_files(css, cgrp, cfts, true);
1544                if (ret < 0) {
1545                        failed_cfts = cfts;
1546                        goto err;
1547                }
1548        }
1549
1550        css->flags |= CSS_VISIBLE;
1551
1552        return 0;
1553err:
1554        list_for_each_entry(cfts, &css->ss->cfts, node) {
1555                if (cfts == failed_cfts)
1556                        break;
1557                cgroup_addrm_files(css, cgrp, cfts, false);
1558        }
1559        return ret;
1560}
1561
1562static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
1563{
1564        struct cgroup *dcgrp = &dst_root->cgrp;
1565        struct cgroup_subsys *ss;
1566        int ssid, i, ret;
1567
1568        lockdep_assert_held(&cgroup_mutex);
1569
1570        do_each_subsys_mask(ss, ssid, ss_mask) {
1571                /*
1572                 * If @ss has non-root csses attached to it, can't move.
1573                 * If @ss is an implicit controller, it is exempt from this
1574                 * rule and can be stolen.
1575                 */
1576                if (css_next_child(NULL, cgroup_css(&ss->root->cgrp, ss)) &&
1577                    !ss->implicit_on_dfl)
1578                        return -EBUSY;
1579
1580                /* can't move between two non-dummy roots either */
1581                if (ss->root != &cgrp_dfl_root && dst_root != &cgrp_dfl_root)
1582                        return -EBUSY;
1583        } while_each_subsys_mask();
1584
1585        do_each_subsys_mask(ss, ssid, ss_mask) {
1586                struct cgroup_root *src_root = ss->root;
1587                struct cgroup *scgrp = &src_root->cgrp;
1588                struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
1589                struct css_set *cset;
1590
1591                WARN_ON(!css || cgroup_css(dcgrp, ss));
1592
1593                /* disable from the source */
1594                src_root->subsys_mask &= ~(1 << ssid);
1595                WARN_ON(cgroup_apply_control(scgrp));
1596                cgroup_finalize_control(scgrp, 0);
1597
1598                /* rebind */
1599                RCU_INIT_POINTER(scgrp->subsys[ssid], NULL);
1600                rcu_assign_pointer(dcgrp->subsys[ssid], css);
1601                ss->root = dst_root;
1602                css->cgroup = dcgrp;
1603
1604                spin_lock_irq(&css_set_lock);
1605                hash_for_each(css_set_table, i, cset, hlist)
1606                        list_move_tail(&cset->e_cset_node[ss->id],
1607                                       &dcgrp->e_csets[ss->id]);
1608                spin_unlock_irq(&css_set_lock);
1609
1610                /* default hierarchy doesn't enable controllers by default */
1611                dst_root->subsys_mask |= 1 << ssid;
1612                if (dst_root == &cgrp_dfl_root) {
1613                        static_branch_enable(cgroup_subsys_on_dfl_key[ssid]);
1614                } else {
1615                        dcgrp->subtree_control |= 1 << ssid;
1616                        static_branch_disable(cgroup_subsys_on_dfl_key[ssid]);
1617                }
1618
1619                ret = cgroup_apply_control(dcgrp);
1620                if (ret)
1621                        pr_warn("partial failure to rebind %s controller (err=%d)\n",
1622                                ss->name, ret);
1623
1624                if (ss->bind)
1625                        ss->bind(css);
1626        } while_each_subsys_mask();
1627
1628        kernfs_activate(dcgrp->kn);
1629        return 0;
1630}
1631
1632static int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
1633                            struct kernfs_root *kf_root)
1634{
1635        int len = 0;
1636        char *buf = NULL;
1637        struct cgroup_root *kf_cgroot = cgroup_root_from_kf(kf_root);
1638        struct cgroup *ns_cgroup;
1639
1640        buf = kmalloc(PATH_MAX, GFP_KERNEL);
1641        if (!buf)
1642                return -ENOMEM;
1643
1644        spin_lock_irq(&css_set_lock);
1645        ns_cgroup = current_cgns_cgroup_from_root(kf_cgroot);
1646        len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX);
1647        spin_unlock_irq(&css_set_lock);
1648
1649        if (len >= PATH_MAX)
1650                len = -ERANGE;
1651        else if (len > 0) {
1652                seq_escape(sf, buf, " \t\n\\");
1653                len = 0;
1654        }
1655        kfree(buf);
1656        return len;
1657}
1658
1659static int cgroup_show_options(struct seq_file *seq,
1660                               struct kernfs_root *kf_root)
1661{
1662        struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1663        struct cgroup_subsys *ss;
1664        int ssid;
1665
1666        if (root != &cgrp_dfl_root)
1667                for_each_subsys(ss, ssid)
1668                        if (root->subsys_mask & (1 << ssid))
1669                                seq_show_option(seq, ss->legacy_name, NULL);
1670        if (root->flags & CGRP_ROOT_NOPREFIX)
1671                seq_puts(seq, ",noprefix");
1672        if (root->flags & CGRP_ROOT_XATTR)
1673                seq_puts(seq, ",xattr");
1674
1675        spin_lock(&release_agent_path_lock);
1676        if (strlen(root->release_agent_path))
1677                seq_show_option(seq, "release_agent",
1678                                root->release_agent_path);
1679        spin_unlock(&release_agent_path_lock);
1680
1681        if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
1682                seq_puts(seq, ",clone_children");
1683        if (strlen(root->name))
1684                seq_show_option(seq, "name", root->name);
1685        return 0;
1686}
1687
1688struct cgroup_sb_opts {
1689        u16 subsys_mask;
1690        unsigned int flags;
1691        char *release_agent;
1692        bool cpuset_clone_children;
1693        char *name;
1694        /* User explicitly requested empty subsystem */
1695        bool none;
1696};
1697
1698static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
1699{
1700        char *token, *o = data;
1701        bool all_ss = false, one_ss = false;
1702        u16 mask = U16_MAX;
1703        struct cgroup_subsys *ss;
1704        int nr_opts = 0;
1705        int i;
1706
1707#ifdef CONFIG_CPUSETS
1708        mask = ~((u16)1 << cpuset_cgrp_id);
1709#endif
1710
1711        memset(opts, 0, sizeof(*opts));
1712
1713        while ((token = strsep(&o, ",")) != NULL) {
1714                nr_opts++;
1715
1716                if (!*token)
1717                        return -EINVAL;
1718                if (!strcmp(token, "none")) {
1719                        /* Explicitly have no subsystems */
1720                        opts->none = true;
1721                        continue;
1722                }
1723                if (!strcmp(token, "all")) {
1724                        /* Mutually exclusive option 'all' + subsystem name */
1725                        if (one_ss)
1726                                return -EINVAL;
1727                        all_ss = true;
1728                        continue;
1729                }
1730                if (!strcmp(token, "noprefix")) {
1731                        opts->flags |= CGRP_ROOT_NOPREFIX;
1732                        continue;
1733                }
1734                if (!strcmp(token, "clone_children")) {
1735                        opts->cpuset_clone_children = true;
1736                        continue;
1737                }
1738                if (!strcmp(token, "xattr")) {
1739                        opts->flags |= CGRP_ROOT_XATTR;
1740                        continue;
1741                }
1742                if (!strncmp(token, "release_agent=", 14)) {
1743                        /* Specifying two release agents is forbidden */
1744                        if (opts->release_agent)
1745                                return -EINVAL;
1746                        opts->release_agent =
1747                                kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
1748                        if (!opts->release_agent)
1749                                return -ENOMEM;
1750                        continue;
1751                }
1752                if (!strncmp(token, "name=", 5)) {
1753                        const char *name = token + 5;
1754                        /* Can't specify an empty name */
1755                        if (!strlen(name))
1756                                return -EINVAL;
1757                        /* Must match [\w.-]+ */
1758                        for (i = 0; i < strlen(name); i++) {
1759                                char c = name[i];
1760                                if (isalnum(c))
1761                                        continue;
1762                                if ((c == '.') || (c == '-') || (c == '_'))
1763                                        continue;
1764                                return -EINVAL;
1765                        }
1766                        /* Specifying two names is forbidden */
1767                        if (opts->name)
1768                                return -EINVAL;
1769                        opts->name = kstrndup(name,
1770                                              MAX_CGROUP_ROOT_NAMELEN - 1,
1771                                              GFP_KERNEL);
1772                        if (!opts->name)
1773                                return -ENOMEM;
1774
1775                        continue;
1776                }
1777
1778                for_each_subsys(ss, i) {
1779                        if (strcmp(token, ss->legacy_name))
1780                                continue;
1781                        if (!cgroup_ssid_enabled(i))
1782                                continue;
1783                        if (cgroup_ssid_no_v1(i))
1784                                continue;
1785
1786                        /* Mutually exclusive option 'all' + subsystem name */
1787                        if (all_ss)
1788                                return -EINVAL;
1789                        opts->subsys_mask |= (1 << i);
1790                        one_ss = true;
1791
1792                        break;
1793                }
1794                if (i == CGROUP_SUBSYS_COUNT)
1795                        return -ENOENT;
1796        }
1797
1798        /*
1799         * If the 'all' option was specified select all the subsystems,
1800         * otherwise if 'none', 'name=' and a subsystem name options were
1801         * not specified, let's default to 'all'
1802         */
1803        if (all_ss || (!one_ss && !opts->none && !opts->name))
1804                for_each_subsys(ss, i)
1805                        if (cgroup_ssid_enabled(i) && !cgroup_ssid_no_v1(i))
1806                                opts->subsys_mask |= (1 << i);
1807
1808        /*
1809         * We either have to specify by name or by subsystems. (So all
1810         * empty hierarchies must have a name).
1811         */
1812        if (!opts->subsys_mask && !opts->name)
1813                return -EINVAL;
1814
1815        /*
1816         * Option noprefix was introduced just for backward compatibility
1817         * with the old cpuset, so we allow noprefix only if mounting just
1818         * the cpuset subsystem.
1819         */
1820        if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
1821                return -EINVAL;
1822
1823        /* Can't specify "none" and some subsystems */
1824        if (opts->subsys_mask && opts->none)
1825                return -EINVAL;
1826
1827        return 0;
1828}
1829
1830static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
1831{
1832        int ret = 0;
1833        struct cgroup_root *root = cgroup_root_from_kf(kf_root);
1834        struct cgroup_sb_opts opts;
1835        u16 added_mask, removed_mask;
1836
1837        if (root == &cgrp_dfl_root) {
1838                pr_err("remount is not allowed\n");
1839                return -EINVAL;
1840        }
1841
1842        cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
1843
1844        /* See what subsystems are wanted */
1845        ret = parse_cgroupfs_options(data, &opts);
1846        if (ret)
1847                goto out_unlock;
1848
1849        if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
1850                pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
1851                        task_tgid_nr(current), current->comm);
1852
1853        added_mask = opts.subsys_mask & ~root->subsys_mask;
1854        removed_mask = root->subsys_mask & ~opts.subsys_mask;
1855
1856        /* Don't allow flags or name to change at remount */
1857        if ((opts.flags ^ root->flags) ||
1858            (opts.name && strcmp(opts.name, root->name))) {
1859                pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
1860                       opts.flags, opts.name ?: "", root->flags, root->name);
1861                ret = -EINVAL;
1862                goto out_unlock;
1863        }
1864
1865        /* remounting is not allowed for populated hierarchies */
1866        if (!list_empty(&root->cgrp.self.children)) {
1867                ret = -EBUSY;
1868                goto out_unlock;
1869        }
1870
1871        ret = rebind_subsystems(root, added_mask);
1872        if (ret)
1873                goto out_unlock;
1874
1875        WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
1876
1877        if (opts.release_agent) {
1878                spin_lock(&release_agent_path_lock);
1879                strcpy(root->release_agent_path, opts.release_agent);
1880                spin_unlock(&release_agent_path_lock);
1881        }
1882
1883        trace_cgroup_remount(root);
1884
1885 out_unlock:
1886        kfree(opts.release_agent);
1887        kfree(opts.name);
1888        mutex_unlock(&cgroup_mutex);
1889        return ret;
1890}
1891
1892/*
1893 * To reduce the fork() overhead for systems that are not actually using
1894 * their cgroups capability, we don't maintain the lists running through
1895 * each css_set to its tasks until we see the list actually used - in other
1896 * words after the first mount.
1897 */
1898static bool use_task_css_set_links __read_mostly;
1899
1900static void cgroup_enable_task_cg_lists(void)
1901{
1902        struct task_struct *p, *g;
1903
1904        spin_lock_irq(&css_set_lock);
1905
1906        if (use_task_css_set_links)
1907                goto out_unlock;
1908
1909        use_task_css_set_links = true;
1910
1911        /*
1912         * We need tasklist_lock because RCU is not safe against
1913         * while_each_thread(). Besides, a forking task that has passed
1914         * cgroup_post_fork() without seeing use_task_css_set_links = 1
1915         * is not guaranteed to have its child immediately visible in the
1916         * tasklist if we walk through it with RCU.
1917         */
1918        read_lock(&tasklist_lock);
1919        do_each_thread(g, p) {
1920                WARN_ON_ONCE(!list_empty(&p->cg_list) ||
1921                             task_css_set(p) != &init_css_set);
1922
1923                /*
1924                 * We should check if the process is exiting, otherwise
1925                 * it will race with cgroup_exit() in that the list
1926                 * entry won't be deleted though the process has exited.
1927                 * Do it while holding siglock so that we don't end up
1928                 * racing against cgroup_exit().
1929                 *
1930                 * Interrupts were already disabled while acquiring
1931                 * the css_set_lock, so we do not need to disable it
1932                 * again when acquiring the sighand->siglock here.
1933                 */
1934                spin_lock(&p->sighand->siglock);
1935                if (!(p->flags & PF_EXITING)) {
1936                        struct css_set *cset = task_css_set(p);
1937
1938                        if (!css_set_populated(cset))
1939                                css_set_update_populated(cset, true);
1940                        list_add_tail(&p->cg_list, &cset->tasks);
1941                        get_css_set(cset);
1942                }
1943                spin_unlock(&p->sighand->siglock);
1944        } while_each_thread(g, p);
1945        read_unlock(&tasklist_lock);
1946out_unlock:
1947        spin_unlock_irq(&css_set_lock);
1948}
1949
1950static void init_cgroup_housekeeping(struct cgroup *cgrp)
1951{
1952        struct cgroup_subsys *ss;
1953        int ssid;
1954
1955        INIT_LIST_HEAD(&cgrp->self.sibling);
1956        INIT_LIST_HEAD(&cgrp->self.children);
1957        INIT_LIST_HEAD(&cgrp->cset_links);
1958        INIT_LIST_HEAD(&cgrp->pidlists);
1959        mutex_init(&cgrp->pidlist_mutex);
1960        cgrp->self.cgroup = cgrp;
1961        cgrp->self.flags |= CSS_ONLINE;
1962
1963        for_each_subsys(ss, ssid)
1964                INIT_LIST_HEAD(&cgrp->e_csets[ssid]);
1965
1966        init_waitqueue_head(&cgrp->offline_waitq);
1967        INIT_WORK(&cgrp->release_agent_work, cgroup_release_agent);
1968}
1969
1970static void init_cgroup_root(struct cgroup_root *root,
1971                             struct cgroup_sb_opts *opts)
1972{
1973        struct cgroup *cgrp = &root->cgrp;
1974
1975        INIT_LIST_HEAD(&root->root_list);
1976        atomic_set(&root->nr_cgrps, 1);
1977        cgrp->root = root;
1978        init_cgroup_housekeeping(cgrp);
1979        idr_init(&root->cgroup_idr);
1980
1981        root->flags = opts->flags;
1982        if (opts->release_agent)
1983                strcpy(root->release_agent_path, opts->release_agent);
1984        if (opts->name)
1985                strcpy(root->name, opts->name);
1986        if (opts->cpuset_clone_children)
1987                set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
1988}
1989
1990static int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
1991{
1992        LIST_HEAD(tmp_links);
1993        struct cgroup *root_cgrp = &root->cgrp;
1994        struct css_set *cset;
1995        int i, ret;
1996
1997        lockdep_assert_held(&cgroup_mutex);
1998
1999        ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
2000        if (ret < 0)
2001                goto out;
2002        root_cgrp->id = ret;
2003        root_cgrp->ancestor_ids[0] = ret;
2004
2005        ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
2006                              GFP_KERNEL);
2007        if (ret)
2008                goto out;
2009
2010        /*
2011         * We're accessing css_set_count without locking css_set_lock here,
2012         * but that's OK - it can only be increased by someone holding
2013         * cgroup_lock, and that's us.  Later rebinding may disable
2014         * controllers on the default hierarchy and thus create new csets,
2015         * which can't be more than the existing ones.  Allocate 2x.
2016         */
2017        ret = allocate_cgrp_cset_links(2 * css_set_count, &tmp_links);
2018        if (ret)
2019                goto cancel_ref;
2020
2021        ret = cgroup_init_root_id(root);
2022        if (ret)
2023                goto cancel_ref;
2024
2025        root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops,
2026                                           KERNFS_ROOT_CREATE_DEACTIVATED,
2027                                           root_cgrp);
2028        if (IS_ERR(root->kf_root)) {
2029                ret = PTR_ERR(root->kf_root);
2030                goto exit_root_id;
2031        }
2032        root_cgrp->kn = root->kf_root->kn;
2033
2034        ret = css_populate_dir(&root_cgrp->self);
2035        if (ret)
2036                goto destroy_root;
2037
2038        ret = rebind_subsystems(root, ss_mask);
2039        if (ret)
2040                goto destroy_root;
2041
2042        trace_cgroup_setup_root(root);
2043
2044        /*
2045         * There must be no failure case after here, since rebinding takes
2046         * care of subsystems' refcounts, which are explicitly dropped in
2047         * the failure exit path.
2048         */
2049        list_add(&root->root_list, &cgroup_roots);
2050        cgroup_root_count++;
2051
2052        /*
2053         * Link the root cgroup in this hierarchy into all the css_set
2054         * objects.
2055         */
2056        spin_lock_irq(&css_set_lock);
2057        hash_for_each(css_set_table, i, cset, hlist) {
2058                link_css_set(&tmp_links, cset, root_cgrp);
2059                if (css_set_populated(cset))
2060                        cgroup_update_populated(root_cgrp, true);
2061        }
2062        spin_unlock_irq(&css_set_lock);
2063
2064        BUG_ON(!list_empty(&root_cgrp->self.children));
2065        BUG_ON(atomic_read(&root->nr_cgrps) != 1);
2066
2067        kernfs_activate(root_cgrp->kn);
2068        ret = 0;
2069        goto out;
2070
2071destroy_root:
2072        kernfs_destroy_root(root->kf_root);
2073        root->kf_root = NULL;
2074exit_root_id:
2075        cgroup_exit_root_id(root);
2076cancel_ref:
2077        percpu_ref_exit(&root_cgrp->self.refcnt);
2078out:
2079        free_cgrp_cset_links(&tmp_links);
2080        return ret;
2081}
2082
2083static struct dentry *cgroup_mount(struct file_system_type *fs_type,
2084                         int flags, const char *unused_dev_name,
2085                         void *data)
2086{
2087        bool is_v2 = fs_type == &cgroup2_fs_type;
2088        struct super_block *pinned_sb = NULL;
2089        struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
2090        struct cgroup_subsys *ss;
2091        struct cgroup_root *root;
2092        struct cgroup_sb_opts opts;
2093        struct dentry *dentry;
2094        int ret;
2095        int i;
2096        bool new_sb;
2097
2098        get_cgroup_ns(ns);
2099
2100        /* Check if the caller has permission to mount. */
2101        if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
2102                put_cgroup_ns(ns);
2103                return ERR_PTR(-EPERM);
2104        }
2105
2106        /*
2107         * The first time anyone tries to mount a cgroup, enable the list
2108         * linking each css_set to its tasks and fix up all existing tasks.
2109         */
2110        if (!use_task_css_set_links)
2111                cgroup_enable_task_cg_lists();
2112
2113        if (is_v2) {
2114                if (data) {
2115                        pr_err("cgroup2: unknown option \"%s\"\n", (char *)data);
2116                        put_cgroup_ns(ns);
2117                        return ERR_PTR(-EINVAL);
2118                }
2119                cgrp_dfl_visible = true;
2120                root = &cgrp_dfl_root;
2121                cgroup_get(&root->cgrp);
2122                goto out_mount;
2123        }
2124
2125        cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
2126
2127        /* First find the desired set of subsystems */
2128        ret = parse_cgroupfs_options(data, &opts);
2129        if (ret)
2130                goto out_unlock;
2131
2132        /*
2133         * Destruction of cgroup root is asynchronous, so subsystems may
2134         * still be dying after the previous unmount.  Let's drain the
2135         * dying subsystems.  We just need to ensure that the ones
2136         * unmounted previously finish dying and don't care about new ones
2137         * starting.  Testing ref liveliness is good enough.
2138         */
2139        for_each_subsys(ss, i) {
2140                if (!(opts.subsys_mask & (1 << i)) ||
2141                    ss->root == &cgrp_dfl_root)
2142                        continue;
2143
2144                if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
2145                        mutex_unlock(&cgroup_mutex);
2146                        msleep(10);
2147                        ret = restart_syscall();
2148                        goto out_free;
2149                }
2150                cgroup_put(&ss->root->cgrp);
2151        }
2152
2153        for_each_root(root) {
2154                bool name_match = false;
2155
2156                if (root == &cgrp_dfl_root)
2157                        continue;
2158
2159                /*
2160                 * If we asked for a name then it must match.  Also, if
2161                 * name matches but sybsys_mask doesn't, we should fail.
2162                 * Remember whether name matched.
2163                 */
2164                if (opts.name) {
2165                        if (strcmp(opts.name, root->name))
2166                                continue;
2167                        name_match = true;
2168                }
2169
2170                /*
2171                 * If we asked for subsystems (or explicitly for no
2172                 * subsystems) then they must match.
2173                 */
2174                if ((opts.subsys_mask || opts.none) &&
2175                    (opts.subsys_mask != root->subsys_mask)) {
2176                        if (!name_match)
2177                                continue;
2178                        ret = -EBUSY;
2179                        goto out_unlock;
2180                }
2181
2182                if (root->flags ^ opts.flags)
2183                        pr_warn("new mount options do not match the existing superblock, will be ignored\n");
2184
2185                /*
2186                 * We want to reuse @root whose lifetime is governed by its
2187                 * ->cgrp.  Let's check whether @root is alive and keep it
2188                 * that way.  As cgroup_kill_sb() can happen anytime, we
2189                 * want to block it by pinning the sb so that @root doesn't
2190                 * get killed before mount is complete.
2191                 *
2192                 * With the sb pinned, tryget_live can reliably indicate
2193                 * whether @root can be reused.  If it's being killed,
2194                 * drain it.  We can use wait_queue for the wait but this
2195                 * path is super cold.  Let's just sleep a bit and retry.
2196                 */
2197                pinned_sb = kernfs_pin_sb(root->kf_root, NULL);
2198                if (IS_ERR(pinned_sb) ||
2199                    !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {
2200                        mutex_unlock(&cgroup_mutex);
2201                        if (!IS_ERR_OR_NULL(pinned_sb))
2202                                deactivate_super(pinned_sb);
2203                        msleep(10);
2204                        ret = restart_syscall();
2205                        goto out_free;
2206                }
2207
2208                ret = 0;
2209                goto out_unlock;
2210        }
2211
2212        /*
2213         * No such thing, create a new one.  name= matching without subsys
2214         * specification is allowed for already existing hierarchies but we
2215         * can't create new one without subsys specification.
2216         */
2217        if (!opts.subsys_mask && !opts.none) {
2218                ret = -EINVAL;
2219                goto out_unlock;
2220        }
2221
2222        /* Hierarchies may only be created in the initial cgroup namespace. */
2223        if (ns != &init_cgroup_ns) {
2224                ret = -EPERM;
2225                goto out_unlock;
2226        }
2227
2228        root = kzalloc(sizeof(*root), GFP_KERNEL);
2229        if (!root) {
2230                ret = -ENOMEM;
2231                goto out_unlock;
2232        }
2233
2234        init_cgroup_root(root, &opts);
2235
2236        ret = cgroup_setup_root(root, opts.subsys_mask);
2237        if (ret)
2238                cgroup_free_root(root);
2239
2240out_unlock:
2241        mutex_unlock(&cgroup_mutex);
2242out_free:
2243        kfree(opts.release_agent);
2244        kfree(opts.name);
2245
2246        if (ret) {
2247                put_cgroup_ns(ns);
2248                return ERR_PTR(ret);
2249        }
2250out_mount:
2251        dentry = kernfs_mount(fs_type, flags, root->kf_root,
2252                              is_v2 ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC,
2253                              &new_sb);
2254
2255        /*
2256         * In non-init cgroup namespace, instead of root cgroup's
2257         * dentry, we return the dentry corresponding to the
2258         * cgroupns->root_cgrp.
2259         */
2260        if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
2261                struct dentry *nsdentry;
2262                struct cgroup *cgrp;
2263
2264                mutex_lock(&cgroup_mutex);
2265                spin_lock_irq(&css_set_lock);
2266
2267                cgrp = cset_cgroup_from_root(ns->root_cset, root);
2268
2269                spin_unlock_irq(&css_set_lock);
2270                mutex_unlock(&cgroup_mutex);
2271
2272                nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
2273                dput(dentry);
2274                dentry = nsdentry;
2275        }
2276
2277        if (IS_ERR(dentry) || !new_sb)
2278                cgroup_put(&root->cgrp);
2279
2280        /*
2281         * If @pinned_sb, we're reusing an existing root and holding an
2282         * extra ref on its sb.  Mount is complete.  Put the extra ref.
2283         */
2284        if (pinned_sb) {
2285                WARN_ON(new_sb);
2286                deactivate_super(pinned_sb);
2287        }
2288
2289        put_cgroup_ns(ns);
2290        return dentry;
2291}
2292
2293static void cgroup_kill_sb(struct super_block *sb)
2294{
2295        struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
2296        struct cgroup_root *root = cgroup_root_from_kf(kf_root);
2297
2298        /*
2299         * If @root doesn't have any mounts or children, start killing it.
2300         * This prevents new mounts by disabling percpu_ref_tryget_live().
2301         * cgroup_mount() may wait for @root's release.
2302         *
2303         * And don't kill the default root.
2304         */
2305        if (!list_empty(&root->cgrp.self.children) ||
2306            root == &cgrp_dfl_root)
2307                cgroup_put(&root->cgrp);
2308        else
2309                percpu_ref_kill(&root->cgrp.self.refcnt);
2310
2311        kernfs_kill_sb(sb);
2312}
2313
2314static struct file_system_type cgroup_fs_type = {
2315        .name = "cgroup",
2316        .mount = cgroup_mount,
2317        .kill_sb = cgroup_kill_sb,
2318        .fs_flags = FS_USERNS_MOUNT,
2319};
2320
2321static struct file_system_type cgroup2_fs_type = {
2322        .name = "cgroup2",
2323        .mount = cgroup_mount,
2324        .kill_sb = cgroup_kill_sb,
2325        .fs_flags = FS_USERNS_MOUNT,
2326};
2327
2328static int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
2329                                 struct cgroup_namespace *ns)
2330{
2331        struct cgroup *root = cset_cgroup_from_root(ns->root_cset, cgrp->root);
2332
2333        return kernfs_path_from_node(cgrp->kn, root->kn, buf, buflen);
2334}
2335
2336int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
2337                   struct cgroup_namespace *ns)
2338{
2339        int ret;
2340
2341        mutex_lock(&cgroup_mutex);
2342        spin_lock_irq(&css_set_lock);
2343
2344        ret = cgroup_path_ns_locked(cgrp, buf, buflen, ns);
2345
2346        spin_unlock_irq(&css_set_lock);
2347        mutex_unlock(&cgroup_mutex);
2348
2349        return ret;
2350}
2351EXPORT_SYMBOL_GPL(cgroup_path_ns);
2352
2353/**
2354 * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
2355 * @task: target task
2356 * @buf: the buffer to write the path into
2357 * @buflen: the length of the buffer
2358 *
2359 * Determine @task's cgroup on the first (the one with the lowest non-zero
2360 * hierarchy_id) cgroup hierarchy and copy its path into @buf.  This
2361 * function grabs cgroup_mutex and shouldn't be used inside locks used by
2362 * cgroup controller callbacks.
2363 *
2364 * Return value is the same as kernfs_path().
2365 */
2366int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
2367{
2368        struct cgroup_root *root;
2369        struct cgroup *cgrp;
2370        int hierarchy_id = 1;
2371        int ret;
2372
2373        mutex_lock(&cgroup_mutex);
2374        spin_lock_irq(&css_set_lock);
2375
2376        root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
2377
2378        if (root) {
2379                cgrp = task_cgroup_from_root(task, root);
2380                ret = cgroup_path_ns_locked(cgrp, buf, buflen, &init_cgroup_ns);
2381        } else {
2382                /* if no hierarchy exists, everyone is in "/" */
2383                ret = strlcpy(buf, "/", buflen);
2384        }
2385
2386        spin_unlock_irq(&css_set_lock);
2387        mutex_unlock(&cgroup_mutex);
2388        return ret;
2389}
2390EXPORT_SYMBOL_GPL(task_cgroup_path);
2391
2392/* used to track tasks and other necessary states during migration */
2393struct cgroup_taskset {
2394        /* the src and dst cset list running through cset->mg_node */
2395        struct list_head        src_csets;
2396        struct list_head        dst_csets;
2397
2398        /* the subsys currently being processed */
2399        int                     ssid;
2400
2401        /*
2402         * Fields for cgroup_taskset_*() iteration.
2403         *
2404         * Before migration is committed, the target migration tasks are on
2405         * ->mg_tasks of the csets on ->src_csets.  After, on ->mg_tasks of
2406         * the csets on ->dst_csets.  ->csets point to either ->src_csets
2407         * or ->dst_csets depending on whether migration is committed.
2408         *
2409         * ->cur_csets and ->cur_task point to the current task position
2410         * during iteration.
2411         */
2412        struct list_head        *csets;
2413        struct css_set          *cur_cset;
2414        struct task_struct      *cur_task;
2415};
2416
2417#define CGROUP_TASKSET_INIT(tset)       (struct cgroup_taskset){        \
2418        .src_csets              = LIST_HEAD_INIT(tset.src_csets),       \
2419        .dst_csets              = LIST_HEAD_INIT(tset.dst_csets),       \
2420        .csets                  = &tset.src_csets,                      \
2421}
2422
2423/**
2424 * cgroup_taskset_add - try to add a migration target task to a taskset
2425 * @task: target task
2426 * @tset: target taskset
2427 *
2428 * Add @task, which is a migration target, to @tset.  This function becomes
2429 * noop if @task doesn't need to be migrated.  @task's css_set should have
2430 * been added as a migration source and @task->cg_list will be moved from
2431 * the css_set's tasks list to mg_tasks one.
2432 */
2433static void cgroup_taskset_add(struct task_struct *task,
2434                               struct cgroup_taskset *tset)
2435{
2436        struct css_set *cset;
2437
2438        lockdep_assert_held(&css_set_lock);
2439
2440        /* @task either already exited or can't exit until the end */
2441        if (task->flags & PF_EXITING)
2442                return;
2443
2444        /* leave @task alone if post_fork() hasn't linked it yet */
2445        if (list_empty(&task->cg_list))
2446                return;
2447
2448        cset = task_css_set(task);
2449        if (!cset->mg_src_cgrp)
2450                return;
2451
2452        list_move_tail(&task->cg_list, &cset->mg_tasks);
2453        if (list_empty(&cset->mg_node))
2454                list_add_tail(&cset->mg_node, &tset->src_csets);
2455        if (list_empty(&cset->mg_dst_cset->mg_node))
2456                list_move_tail(&cset->mg_dst_cset->mg_node,
2457                               &tset->dst_csets);
2458}
2459
2460/**
2461 * cgroup_taskset_first - reset taskset and return the first task
2462 * @tset: taskset of interest
2463 * @dst_cssp: output variable for the destination css
2464 *
2465 * @tset iteration is initialized and the first task is returned.
2466 */
2467struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset,
2468                                         struct cgroup_subsys_state **dst_cssp)
2469{
2470        tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node);
2471        tset->cur_task = NULL;
2472
2473        return cgroup_taskset_next(tset, dst_cssp);
2474}
2475
2476/**
2477 * cgroup_taskset_next - iterate to the next task in taskset
2478 * @tset: taskset of interest
2479 * @dst_cssp: output variable for the destination css
2480 *
2481 * Return the next task in @tset.  Iteration must have been initialized
2482 * with cgroup_taskset_first().
2483 */
2484struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
2485                                        struct cgroup_subsys_state **dst_cssp)
2486{
2487        struct css_set *cset = tset->cur_cset;
2488        struct task_struct *task = tset->cur_task;
2489
2490        while (&cset->mg_node != tset->csets) {
2491                if (!task)
2492                        task = list_first_entry(&cset->mg_tasks,
2493                                                struct task_struct, cg_list);
2494                else
2495                        task = list_next_entry(task, cg_list);
2496
2497                if (&task->cg_list != &cset->mg_tasks) {
2498                        tset->cur_cset = cset;
2499                        tset->cur_task = task;
2500
2501                        /*
2502                         * This function may be called both before and
2503                         * after cgroup_taskset_migrate().  The two cases
2504                         * can be distinguished by looking at whether @cset
2505                         * has its ->mg_dst_cset set.
2506                         */
2507                        if (cset->mg_dst_cset)
2508                                *dst_cssp = cset->mg_dst_cset->subsys[tset->ssid];
2509                        else
2510                                *dst_cssp = cset->subsys[tset->ssid];
2511
2512                        return task;
2513                }
2514
2515                cset = list_next_entry(cset, mg_node);
2516                task = NULL;
2517        }
2518
2519        return NULL;
2520}
2521
2522/**
2523 * cgroup_taskset_migrate - migrate a taskset
2524 * @tset: taget taskset
2525 * @root: cgroup root the migration is taking place on
2526 *
2527 * Migrate tasks in @tset as setup by migration preparation functions.
2528 * This function fails iff one of the ->can_attach callbacks fails and
2529 * guarantees that either all or none of the tasks in @tset are migrated.
2530 * @tset is consumed regardless of success.
2531 */
2532static int cgroup_taskset_migrate(struct cgroup_taskset *tset,
2533                                  struct cgroup_root *root)
2534{
2535        struct cgroup_subsys *ss;
2536        struct task_struct *task, *tmp_task;
2537        struct css_set *cset, *tmp_cset;
2538        int ssid, failed_ssid, ret;
2539
2540        /* methods shouldn't be called if no task is actually migrating */
2541        if (list_empty(&tset->src_csets))
2542                return 0;
2543
2544        /* check that we can legitimately attach to the cgroup */
2545        do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2546                if (ss->can_attach) {
2547                        tset->ssid = ssid;
2548                        ret = ss->can_attach(tset);
2549                        if (ret) {
2550                                failed_ssid = ssid;
2551                                goto out_cancel_attach;
2552                        }
2553                }
2554        } while_each_subsys_mask();
2555
2556        /*
2557         * Now that we're guaranteed success, proceed to move all tasks to
2558         * the new cgroup.  There are no failure cases after here, so this
2559         * is the commit point.
2560         */
2561        spin_lock_irq(&css_set_lock);
2562        list_for_each_entry(cset, &tset->src_csets, mg_node) {
2563                list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) {
2564                        struct css_set *from_cset = task_css_set(task);
2565                        struct css_set *to_cset = cset->mg_dst_cset;
2566
2567                        get_css_set(to_cset);
2568                        css_set_move_task(task, from_cset, to_cset, true);
2569                        put_css_set_locked(from_cset);
2570                }
2571        }
2572        spin_unlock_irq(&css_set_lock);
2573
2574        /*
2575         * Migration is committed, all target tasks are now on dst_csets.
2576         * Nothing is sensitive to fork() after this point.  Notify
2577         * controllers that migration is complete.
2578         */
2579        tset->csets = &tset->dst_csets;
2580
2581        do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2582                if (ss->attach) {
2583                        tset->ssid = ssid;
2584                        ss->attach(tset);
2585                }
2586        } while_each_subsys_mask();
2587
2588        ret = 0;
2589        goto out_release_tset;
2590
2591out_cancel_attach:
2592        do_each_subsys_mask(ss, ssid, root->subsys_mask) {
2593                if (ssid == failed_ssid)
2594                        break;
2595                if (ss->cancel_attach) {
2596                        tset->ssid = ssid;
2597                        ss->cancel_attach(tset);
2598                }
2599        } while_each_subsys_mask();
2600out_release_tset:
2601        spin_lock_irq(&css_set_lock);
2602        list_splice_init(&tset->dst_csets, &tset->src_csets);
2603        list_for_each_entry_safe(cset, tmp_cset, &tset->src_csets, mg_node) {
2604                list_splice_tail_init(&cset->mg_tasks, &cset->tasks);
2605                list_del_init(&cset->mg_node);
2606        }
2607        spin_unlock_irq(&css_set_lock);
2608        return ret;
2609}
2610
2611/**
2612 * cgroup_may_migrate_to - verify whether a cgroup can be migration destination
2613 * @dst_cgrp: destination cgroup to test
2614 *
2615 * On the default hierarchy, except for the root, subtree_control must be
2616 * zero for migration destination cgroups with tasks so that child cgroups
2617 * don't compete against tasks.
2618 */
2619static bool cgroup_may_migrate_to(struct cgroup *dst_cgrp)
2620{
2621        return !cgroup_on_dfl(dst_cgrp) || !cgroup_parent(dst_cgrp) ||
2622                !dst_cgrp->subtree_control;
2623}
2624
2625/**
2626 * cgroup_migrate_finish - cleanup after attach
2627 * @preloaded_csets: list of preloaded css_sets
2628 *
2629 * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst().  See
2630 * those functions for details.
2631 */
2632static void cgroup_migrate_finish(struct list_head *preloaded_csets)
2633{
2634        struct css_set *cset, *tmp_cset;
2635
2636        lockdep_assert_held(&cgroup_mutex);
2637
2638        spin_lock_irq(&css_set_lock);
2639        list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) {
2640                cset->mg_src_cgrp = NULL;
2641                cset->mg_dst_cgrp = NULL;
2642                cset->mg_dst_cset = NULL;
2643                list_del_init(&cset->mg_preload_node);
2644                put_css_set_locked(cset);
2645        }
2646        spin_unlock_irq(&css_set_lock);
2647}
2648
2649/**
2650 * cgroup_migrate_add_src - add a migration source css_set
2651 * @src_cset: the source css_set to add
2652 * @dst_cgrp: the destination cgroup
2653 * @preloaded_csets: list of preloaded css_sets
2654 *
2655 * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp.  Pin
2656 * @src_cset and add it to @preloaded_csets, which should later be cleaned
2657 * up by cgroup_migrate_finish().
2658 *
2659 * This function may be called without holding cgroup_threadgroup_rwsem
2660 * even if the target is a process.  Threads may be created and destroyed
2661 * but as long as cgroup_mutex is not dropped, no new css_set can be put
2662 * into play and the preloaded css_sets are guaranteed to cover all
2663 * migrations.
2664 */
2665static void cgroup_migrate_add_src(struct css_set *src_cset,
2666                                   struct cgroup *dst_cgrp,
2667                                   struct list_head *preloaded_csets)
2668{
2669        struct cgroup *src_cgrp;
2670
2671        lockdep_assert_held(&cgroup_mutex);
2672        lockdep_assert_held(&css_set_lock);
2673
2674        /*
2675         * If ->dead, @src_set is associated with one or more dead cgroups
2676         * and doesn't contain any migratable tasks.  Ignore it early so
2677         * that the rest of migration path doesn't get confused by it.
2678         */
2679        if (src_cset->dead)
2680                return;
2681
2682        src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root);
2683
2684        if (!list_empty(&src_cset->mg_preload_node))
2685                return;
2686
2687        WARN_ON(src_cset->mg_src_cgrp);
2688        WARN_ON(src_cset->mg_dst_cgrp);
2689        WARN_ON(!list_empty(&src_cset->mg_tasks));
2690        WARN_ON(!list_empty(&src_cset->mg_node));
2691
2692        src_cset->mg_src_cgrp = src_cgrp;
2693        src_cset->mg_dst_cgrp = dst_cgrp;
2694        get_css_set(src_cset);
2695        list_add(&src_cset->mg_preload_node, preloaded_csets);
2696}
2697
2698/**
2699 * cgroup_migrate_prepare_dst - prepare destination css_sets for migration
2700 * @preloaded_csets: list of preloaded source css_sets
2701 *
2702 * Tasks are about to be moved and all the source css_sets have been
2703 * preloaded to @preloaded_csets.  This function looks up and pins all
2704 * destination css_sets, links each to its source, and append them to
2705 * @preloaded_csets.
2706 *
2707 * This function must be called after cgroup_migrate_add_src() has been
2708 * called on each migration source css_set.  After migration is performed
2709 * using cgroup_migrate(), cgroup_migrate_finish() must be called on
2710 * @preloaded_csets.
2711 */
2712static int cgroup_migrate_prepare_dst(struct list_head *preloaded_csets)
2713{
2714        LIST_HEAD(csets);
2715        struct css_set *src_cset, *tmp_cset;
2716
2717        lockdep_assert_held(&cgroup_mutex);
2718
2719        /* look up the dst cset for each src cset and link it to src */
2720        list_for_each_entry_safe(src_cset, tmp_cset, preloaded_csets, mg_preload_node) {
2721                struct css_set *dst_cset;
2722
2723                dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);
2724                if (!dst_cset)
2725                        goto err;
2726
2727                WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset);
2728
2729                /*
2730                 * If src cset equals dst, it's noop.  Drop the src.
2731                 * cgroup_migrate() will skip the cset too.  Note that we
2732                 * can't handle src == dst as some nodes are used by both.
2733                 */
2734                if (src_cset == dst_cset) {
2735                        src_cset->mg_src_cgrp = NULL;
2736                        src_cset->mg_dst_cgrp = NULL;
2737                        list_del_init(&src_cset->mg_preload_node);
2738                        put_css_set(src_cset);
2739                        put_css_set(dst_cset);
2740                        continue;
2741                }
2742
2743                src_cset->mg_dst_cset = dst_cset;
2744
2745                if (list_empty(&dst_cset->mg_preload_node))
2746                        list_add(&dst_cset->mg_preload_node, &csets);
2747                else
2748                        put_css_set(dst_cset);
2749        }
2750
2751        list_splice_tail(&csets, preloaded_csets);
2752        return 0;
2753err:
2754        cgroup_migrate_finish(&csets);
2755        return -ENOMEM;
2756}
2757
2758/**
2759 * cgroup_migrate - migrate a process or task to a cgroup
2760 * @leader: the leader of the process or the task to migrate
2761 * @threadgroup: whether @leader points to the whole process or a single task
2762 * @root: cgroup root migration is taking place on
2763 *
2764 * Migrate a process or task denoted by @leader.  If migrating a process,
2765 * the caller must be holding cgroup_threadgroup_rwsem.  The caller is also
2766 * responsible for invoking cgroup_migrate_add_src() and
2767 * cgroup_migrate_prepare_dst() on the targets before invoking this
2768 * function and following up with cgroup_migrate_finish().
2769 *
2770 * As long as a controller's ->can_attach() doesn't fail, this function is
2771 * guaranteed to succeed.  This means that, excluding ->can_attach()
2772 * failure, when migrating multiple targets, the success or failure can be
2773 * decided for all targets by invoking group_migrate_prepare_dst() before
2774 * actually starting migrating.
2775 */
2776static int cgroup_migrate(struct task_struct *leader, bool threadgroup,
2777                          struct cgroup_root *root)
2778{
2779        struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
2780        struct task_struct *task;
2781
2782        /*
2783         * Prevent freeing of tasks while we take a snapshot. Tasks that are
2784         * already PF_EXITING could be freed from underneath us unless we
2785         * take an rcu_read_lock.
2786         */
2787        spin_lock_irq(&css_set_lock);
2788        rcu_read_lock();
2789        task = leader;
2790        do {
2791                cgroup_taskset_add(task, &tset);
2792                if (!threadgroup)
2793                        break;
2794        } while_each_thread(leader, task);
2795        rcu_read_unlock();
2796        spin_unlock_irq(&css_set_lock);
2797
2798        return cgroup_taskset_migrate(&tset, root);
2799}
2800
2801/**
2802 * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup
2803 * @dst_cgrp: the cgroup to attach to
2804 * @leader: the task or the leader of the threadgroup to be attached
2805 * @threadgroup: attach the whole threadgroup?
2806 *
2807 * Call holding cgroup_mutex and cgroup_threadgroup_rwsem.
2808 */
2809static int cgroup_attach_task(struct cgroup *dst_cgrp,
2810                              struct task_struct *leader, bool threadgroup)
2811{
2812        LIST_HEAD(preloaded_csets);
2813        struct task_struct *task;
2814        int ret;
2815
2816        if (!cgroup_may_migrate_to(dst_cgrp))
2817                return -EBUSY;
2818
2819        /* look up all src csets */
2820        spin_lock_irq(&css_set_lock);
2821        rcu_read_lock();
2822        task = leader;
2823        do {
2824                cgroup_migrate_add_src(task_css_set(task), dst_cgrp,
2825                                       &preloaded_csets);
2826                if (!threadgroup)
2827                        break;
2828        } while_each_thread(leader, task);
2829        rcu_read_unlock();
2830        spin_unlock_irq(&css_set_lock);
2831
2832        /* prepare dst csets and commit */
2833        ret = cgroup_migrate_prepare_dst(&preloaded_csets);
2834        if (!ret)
2835                ret = cgroup_migrate(leader, threadgroup, dst_cgrp->root);
2836
2837        cgroup_migrate_finish(&preloaded_csets);
2838
2839        if (!ret)
2840                trace_cgroup_attach_task(dst_cgrp, leader, threadgroup);
2841
2842        return ret;
2843}
2844
2845static int cgroup_procs_write_permission(struct task_struct *task,
2846                                         struct cgroup *dst_cgrp,
2847                                         struct kernfs_open_file *of)
2848{
2849        const struct cred *cred = current_cred();
2850        const struct cred *tcred = get_task_cred(task);
2851        int ret = 0;
2852
2853        /*
2854         * even if we're attaching all tasks in the thread group, we only
2855         * need to check permissions on one of them.
2856         */
2857        if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
2858            !uid_eq(cred->euid, tcred->uid) &&
2859            !uid_eq(cred->euid, tcred->suid))
2860                ret = -EACCES;
2861
2862        if (!ret && cgroup_on_dfl(dst_cgrp)) {
2863                struct super_block *sb = of->file->f_path.dentry->d_sb;
2864                struct cgroup *cgrp;
2865                struct inode *inode;
2866
2867                spin_lock_irq(&css_set_lock);
2868                cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
2869                spin_unlock_irq(&css_set_lock);
2870
2871                while (!cgroup_is_descendant(dst_cgrp, cgrp))
2872                        cgrp = cgroup_parent(cgrp);
2873
2874                ret = -ENOMEM;
2875                inode = kernfs_get_inode(sb, cgrp->procs_file.kn);
2876                if (inode) {
2877                        ret = inode_permission(inode, MAY_WRITE);
2878                        iput(inode);
2879                }
2880        }
2881
2882        put_cred(tcred);
2883        return ret;
2884}
2885
2886/*
2887 * Find the task_struct of the task to attach by vpid and pass it along to the
2888 * function to attach either it or all tasks in its threadgroup. Will lock
2889 * cgroup_mutex and threadgroup.
2890 */
2891static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
2892                                    size_t nbytes, loff_t off, bool threadgroup)
2893{
2894        struct task_struct *tsk;
2895        struct cgroup_subsys *ss;
2896        struct cgroup *cgrp;
2897        pid_t pid;
2898        int ssid, ret;
2899
2900        if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
2901                return -EINVAL;
2902
2903        cgrp = cgroup_kn_lock_live(of->kn, false);
2904        if (!cgrp)
2905                return -ENODEV;
2906
2907        percpu_down_write(&cgroup_threadgroup_rwsem);
2908        rcu_read_lock();
2909        if (pid) {
2910                tsk = find_task_by_vpid(pid);
2911                if (!tsk) {
2912                        ret = -ESRCH;
2913                        goto out_unlock_rcu;
2914                }
2915        } else {
2916                tsk = current;
2917        }
2918
2919        if (threadgroup)
2920                tsk = tsk->group_leader;
2921
2922        /*
2923         * Workqueue threads may acquire PF_NO_SETAFFINITY and become
2924         * trapped in a cpuset, or RT worker may be born in a cgroup
2925         * with no rt_runtime allocated.  Just say no.
2926         */
2927        if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
2928                ret = -EINVAL;
2929                goto out_unlock_rcu;
2930        }
2931
2932        get_task_struct(tsk);
2933        rcu_read_unlock();
2934
2935        ret = cgroup_procs_write_permission(tsk, cgrp, of);
2936        if (!ret)
2937                ret = cgroup_attach_task(cgrp, tsk, threadgroup);
2938
2939        put_task_struct(tsk);
2940        goto out_unlock_threadgroup;
2941
2942out_unlock_rcu:
2943        rcu_read_unlock();
2944out_unlock_threadgroup:
2945        percpu_up_write(&cgroup_threadgroup_rwsem);
2946        for_each_subsys(ss, ssid)
2947                if (ss->post_attach)
2948                        ss->post_attach();
2949        cgroup_kn_unlock(of->kn);
2950        return ret ?: nbytes;
2951}
2952
2953/**
2954 * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from'
2955 * @from: attach to all cgroups of a given task
2956 * @tsk: the task to be attached
2957 */
2958int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
2959{
2960        struct cgroup_root *root;
2961        int retval = 0;
2962
2963        mutex_lock(&cgroup_mutex);
2964        percpu_down_write(&cgroup_threadgroup_rwsem);
2965        for_each_root(root) {
2966                struct cgroup *from_cgrp;
2967
2968                if (root == &cgrp_dfl_root)
2969                        continue;
2970
2971                spin_lock_irq(&css_set_lock);
2972                from_cgrp = task_cgroup_from_root(from, root);
2973                spin_unlock_irq(&css_set_lock);
2974
2975                retval = cgroup_attach_task(from_cgrp, tsk, false);
2976                if (retval)
2977                        break;
2978        }
2979        percpu_up_write(&cgroup_threadgroup_rwsem);
2980        mutex_unlock(&cgroup_mutex);
2981
2982        return retval;
2983}
2984EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
2985
2986static ssize_t cgroup_tasks_write(struct kernfs_open_file *of,
2987                                  char *buf, size_t nbytes, loff_t off)
2988{
2989        return __cgroup_procs_write(of, buf, nbytes, off, false);
2990}
2991
2992static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
2993                                  char *buf, size_t nbytes, loff_t off)
2994{
2995        return __cgroup_procs_write(of, buf, nbytes, off, true);
2996}
2997
2998static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
2999                                          char *buf, size_t nbytes, loff_t off)
3000{
3001        struct cgroup *cgrp;
3002
3003        BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
3004
3005        cgrp = cgroup_kn_lock_live(of->kn, false);
3006        if (!cgrp)
3007                return -ENODEV;
3008        spin_lock(&release_agent_path_lock);
3009        strlcpy(cgrp->root->release_agent_path, strstrip(buf),
3010                sizeof(cgrp->root->release_agent_path));
3011        spin_unlock(&release_agent_path_lock);
3012        cgroup_kn_unlock(of->kn);
3013        return nbytes;
3014}
3015
3016static int cgroup_release_agent_show(struct seq_file *seq, void *v)
3017{
3018        struct cgroup *cgrp = seq_css(seq)->cgroup;
3019
3020        spin_lock(&release_agent_path_lock);
3021        seq_puts(seq, cgrp->root->release_agent_path);
3022        spin_unlock(&release_agent_path_lock);
3023        seq_putc(seq, '\n');
3024        return 0;
3025}
3026
3027static int cgroup_sane_behavior_show(struct seq_file *seq, void *v)
3028{
3029        seq_puts(seq, "0\n");
3030        return 0;
3031}
3032
3033static void cgroup_print_ss_mask(struct seq_file *seq, u16 ss_mask)
3034{
3035        struct cgroup_subsys *ss;
3036        bool printed = false;
3037        int ssid;
3038
3039        do_each_subsys_mask(ss, ssid, ss_mask) {
3040                if (printed)
3041                        seq_putc(seq, ' ');
3042                seq_printf(seq, "%s", ss->name);
3043                printed = true;
3044        } while_each_subsys_mask();
3045        if (printed)
3046                seq_putc(seq, '\n');
3047}
3048
3049/* show controllers which are enabled from the parent */
3050static int cgroup_controllers_show(struct seq_file *seq, void *v)
3051{
3052        struct cgroup *cgrp = seq_css(seq)->cgroup;
3053
3054        cgroup_print_ss_mask(seq, cgroup_control(cgrp));
3055        return 0;
3056}
3057
3058/* show controllers which are enabled for a given cgroup's children */
3059static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
3060{
3061        struct cgroup *cgrp = seq_css(seq)->cgroup;
3062
3063        cgroup_print_ss_mask(seq, cgrp->subtree_control);
3064        return 0;
3065}
3066
3067/**
3068 * cgroup_update_dfl_csses - update css assoc of a subtree in default hierarchy
3069 * @cgrp: root of the subtree to update csses for
3070 *
3071 * @cgrp's control masks have changed and its subtree's css associations
3072 * need to be updated accordingly.  This function looks up all css_sets
3073 * which are attached to the subtree, creates the matching updated css_sets
3074 * and migrates the tasks to the new ones.
3075 */
3076static int cgroup_update_dfl_csses(struct cgroup *cgrp)
3077{
3078        LIST_HEAD(preloaded_csets);
3079        struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
3080        struct cgroup_subsys_state *d_css;
3081        struct cgroup *dsct;
3082        struct css_set *src_cset;
3083        int ret;
3084
3085        lockdep_assert_held(&cgroup_mutex);
3086
3087        percpu_down_write(&cgroup_threadgroup_rwsem);
3088
3089        /* look up all csses currently attached to @cgrp's subtree */
3090        spin_lock_irq(&css_set_lock);
3091        cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3092                struct cgrp_cset_link *link;
3093
3094                list_for_each_entry(link, &dsct->cset_links, cset_link)
3095                        cgroup_migrate_add_src(link->cset, dsct,
3096                                               &preloaded_csets);
3097        }
3098        spin_unlock_irq(&css_set_lock);
3099
3100        /* NULL dst indicates self on default hierarchy */
3101        ret = cgroup_migrate_prepare_dst(&preloaded_csets);
3102        if (ret)
3103                goto out_finish;
3104
3105        spin_lock_irq(&css_set_lock);
3106        list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
3107                struct task_struct *task, *ntask;
3108
3109                /* src_csets precede dst_csets, break on the first dst_cset */
3110                if (!src_cset->mg_src_cgrp)
3111                        break;
3112
3113                /* all tasks in src_csets need to be migrated */
3114                list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
3115                        cgroup_taskset_add(task, &tset);
3116        }
3117        spin_unlock_irq(&css_set_lock);
3118
3119        ret = cgroup_taskset_migrate(&tset, cgrp->root);
3120out_finish:
3121        cgroup_migrate_finish(&preloaded_csets);
3122        percpu_up_write(&cgroup_threadgroup_rwsem);
3123        return ret;
3124}
3125
3126/**
3127 * cgroup_lock_and_drain_offline - lock cgroup_mutex and drain offlined csses
3128 * @cgrp: root of the target subtree
3129 *
3130 * Because css offlining is asynchronous, userland may try to re-enable a
3131 * controller while the previous css is still around.  This function grabs
3132 * cgroup_mutex and drains the previous css instances of @cgrp's subtree.
3133 */
3134static void cgroup_lock_and_drain_offline(struct cgroup *cgrp)
3135        __acquires(&cgroup_mutex)
3136{
3137        struct cgroup *dsct;
3138        struct cgroup_subsys_state *d_css;
3139        struct cgroup_subsys *ss;
3140        int ssid;
3141
3142restart:
3143        mutex_lock(&cgroup_mutex);
3144
3145        cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3146                for_each_subsys(ss, ssid) {
3147                        struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3148                        DEFINE_WAIT(wait);
3149
3150                        if (!css || !percpu_ref_is_dying(&css->refcnt))
3151                                continue;
3152
3153                        cgroup_get(dsct);
3154                        prepare_to_wait(&dsct->offline_waitq, &wait,
3155                                        TASK_UNINTERRUPTIBLE);
3156
3157                        mutex_unlock(&cgroup_mutex);
3158                        schedule();
3159                        finish_wait(&dsct->offline_waitq, &wait);
3160
3161                        cgroup_put(dsct);
3162                        goto restart;
3163                }
3164        }
3165}
3166
3167/**
3168 * cgroup_save_control - save control masks of a subtree
3169 * @cgrp: root of the target subtree
3170 *
3171 * Save ->subtree_control and ->subtree_ss_mask to the respective old_
3172 * prefixed fields for @cgrp's subtree including @cgrp itself.
3173 */
3174static void cgroup_save_control(struct cgroup *cgrp)
3175{
3176        struct cgroup *dsct;
3177        struct cgroup_subsys_state *d_css;
3178
3179        cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3180                dsct->old_subtree_control = dsct->subtree_control;
3181                dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
3182        }
3183}
3184
3185/**
3186 * cgroup_propagate_control - refresh control masks of a subtree
3187 * @cgrp: root of the target subtree
3188 *
3189 * For @cgrp and its subtree, ensure ->subtree_ss_mask matches
3190 * ->subtree_control and propagate controller availability through the
3191 * subtree so that descendants don't have unavailable controllers enabled.
3192 */
3193static void cgroup_propagate_control(struct cgroup *cgrp)
3194{
3195        struct cgroup *dsct;
3196        struct cgroup_subsys_state *d_css;
3197
3198        cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3199                dsct->subtree_control &= cgroup_control(dsct);
3200                dsct->subtree_ss_mask =
3201                        cgroup_calc_subtree_ss_mask(dsct->subtree_control,
3202                                                    cgroup_ss_mask(dsct));
3203        }
3204}
3205
3206/**
3207 * cgroup_restore_control - restore control masks of a subtree
3208 * @cgrp: root of the target subtree
3209 *
3210 * Restore ->subtree_control and ->subtree_ss_mask from the respective old_
3211 * prefixed fields for @cgrp's subtree including @cgrp itself.
3212 */
3213static void cgroup_restore_control(struct cgroup *cgrp)
3214{
3215        struct cgroup *dsct;
3216        struct cgroup_subsys_state *d_css;
3217
3218        cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3219                dsct->subtree_control = dsct->old_subtree_control;
3220                dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
3221        }
3222}
3223
3224static bool css_visible(struct cgroup_subsys_state *css)
3225{
3226        struct cgroup_subsys *ss = css->ss;
3227        struct cgroup *cgrp = css->cgroup;
3228
3229        if (cgroup_control(cgrp) & (1 << ss->id))
3230                return true;
3231        if (!(cgroup_ss_mask(cgrp) & (1 << ss->id)))
3232                return false;
3233        return cgroup_on_dfl(cgrp) && ss->implicit_on_dfl;
3234}
3235
3236/**
3237 * cgroup_apply_control_enable - enable or show csses according to control
3238 * @cgrp: root of the target subtree
3239 *
3240 * Walk @cgrp's subtree and create new csses or make the existing ones
3241 * visible.  A css is created invisible if it's being implicitly enabled
3242 * through dependency.  An invisible css is made visible when the userland
3243 * explicitly enables it.
3244 *
3245 * Returns 0 on success, -errno on failure.  On failure, csses which have
3246 * been processed already aren't cleaned up.  The caller is responsible for
3247 * cleaning up with cgroup_apply_control_disble().
3248 */
3249static int cgroup_apply_control_enable(struct cgroup *cgrp)
3250{
3251        struct cgroup *dsct;
3252        struct cgroup_subsys_state *d_css;
3253        struct cgroup_subsys *ss;
3254        int ssid, ret;
3255
3256        cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
3257                for_each_subsys(ss, ssid) {
3258                        struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3259
3260                        WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3261
3262                        if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
3263                                continue;
3264
3265                        if (!css) {
3266                                css = css_create(dsct, ss);
3267                                if (IS_ERR(css))
3268                                        return PTR_ERR(css);
3269                        }
3270
3271                        if (css_visible(css)) {
3272                                ret = css_populate_dir(css);
3273                                if (ret)
3274                                        return ret;
3275                        }
3276                }
3277        }
3278
3279        return 0;
3280}
3281
3282/**
3283 * cgroup_apply_control_disable - kill or hide csses according to control
3284 * @cgrp: root of the target subtree
3285 *
3286 * Walk @cgrp's subtree and kill and hide csses so that they match
3287 * cgroup_ss_mask() and cgroup_visible_mask().
3288 *
3289 * A css is hidden when the userland requests it to be disabled while other
3290 * subsystems are still depending on it.  The css must not actively control
3291 * resources and be in the vanilla state if it's made visible again later.
3292 * Controllers which may be depended upon should provide ->css_reset() for
3293 * this purpose.
3294 */
3295static void cgroup_apply_control_disable(struct cgroup *cgrp)
3296{
3297        struct cgroup *dsct;
3298        struct cgroup_subsys_state *d_css;
3299        struct cgroup_subsys *ss;
3300        int ssid;
3301
3302        cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
3303                for_each_subsys(ss, ssid) {
3304                        struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
3305
3306                        WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt));
3307
3308                        if (!css)
3309                                continue;
3310
3311                        if (css->parent &&
3312                            !(cgroup_ss_mask(dsct) & (1 << ss->id))) {
3313                                kill_css(css);
3314                        } else if (!css_visible(css)) {
3315                                css_clear_dir(css);
3316                                if (ss->css_reset)
3317                                        ss->css_reset(css);
3318                        }
3319                }
3320        }
3321}
3322
3323/**
3324 * cgroup_apply_control - apply control mask updates to the subtree
3325 * @cgrp: root of the target subtree
3326 *
3327 * subsystems can be enabled and disabled in a subtree using the following
3328 * steps.
3329 *
3330 * 1. Call cgroup_save_control() to stash the current state.
3331 * 2. Update ->subtree_control masks in the subtree as desired.
3332 * 3. Call cgroup_apply_control() to apply the changes.
3333 * 4. Optionally perform other related operations.
3334 * 5. Call cgroup_finalize_control() to finish up.
3335 *
3336 * This function implements step 3 and propagates the mask changes
3337 * throughout @cgrp's subtree, updates csses accordingly and perform
3338 * process migrations.
3339 */
3340static int cgroup_apply_control(struct cgroup *cgrp)
3341{
3342        int ret;
3343
3344        cgroup_propagate_control(cgrp);
3345
3346        ret = cgroup_apply_control_enable(cgrp);
3347        if (ret)
3348                return ret;
3349
3350        /*
3351         * At this point, cgroup_e_css() results reflect the new csses
3352         * making the following cgroup_update_dfl_csses() properly update
3353         * css associations of all tasks in the subtree.
3354         */
3355        ret = cgroup_update_dfl_csses(cgrp);
3356        if (ret)
3357                return ret;
3358
3359        return 0;
3360}
3361
3362/**
3363 * cgroup_finalize_control - finalize control mask update
3364 * @cgrp: root of the target subtree
3365 * @ret: the result of the update
3366 *
3367 * Finalize control mask update.  See cgroup_apply_control() for more info.
3368 */
3369static void cgroup_finalize_control(struct cgroup *cgrp, int ret)
3370{
3371        if (ret) {
3372                cgroup_restore_control(cgrp);
3373                cgroup_propagate_control(cgrp);
3374        }
3375
3376        cgroup_apply_control_disable(cgrp);
3377}
3378
3379/* change the enabled child controllers for a cgroup in the default hierarchy */
3380static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
3381                                            char *buf, size_t nbytes,
3382                                            loff_t off)
3383{
3384        u16 enable = 0, disable = 0;
3385        struct cgroup *cgrp, *child;
3386        struct cgroup_subsys *ss;
3387        char *tok;
3388        int ssid, ret;
3389
3390        /*
3391         * Parse input - space separated list of subsystem names prefixed
3392         * with either + or -.
3393         */
3394        buf = strstrip(buf);
3395        while ((tok = strsep(&buf, " "))) {
3396                if (tok[0] == '\0')
3397                        continue;
3398                do_each_subsys_mask(ss, ssid, ~cgrp_dfl_inhibit_ss_mask) {
3399                        if (!cgroup_ssid_enabled(ssid) ||
3400                            strcmp(tok + 1, ss->name))
3401                                continue;
3402
3403                        if (*tok == '+') {
3404                                enable |= 1 << ssid;
3405                                disable &= ~(1 << ssid);
3406                        } else if (*tok == '-') {
3407                                disable |= 1 << ssid;
3408                                enable &= ~(1 << ssid);
3409                        } else {
3410                                return -EINVAL;
3411                        }
3412                        break;
3413                } while_each_subsys_mask();
3414                if (ssid == CGROUP_SUBSYS_COUNT)
3415                        return -EINVAL;
3416        }
3417
3418        cgrp = cgroup_kn_lock_live(of->kn, true);
3419        if (!cgrp)
3420                return -ENODEV;
3421
3422        for_each_subsys(ss, ssid) {
3423                if (enable & (1 << ssid)) {
3424                        if (cgrp->subtree_control & (1 << ssid)) {
3425                                enable &= ~(1 << ssid);
3426                                continue;
3427                        }
3428
3429                        if (!(cgroup_control(cgrp) & (1 << ssid))) {
3430                                ret = -ENOENT;
3431                                goto out_unlock;
3432                        }
3433                } else if (disable & (1 << ssid)) {
3434                        if (!(cgrp->subtree_control & (1 << ssid))) {
3435                                disable &= ~(1 << ssid);
3436                                continue;
3437                        }
3438
3439                        /* a child has it enabled? */
3440                        cgroup_for_each_live_child(child, cgrp) {
3441                                if (child->subtree_control & (1 << ssid)) {
3442                                        ret = -EBUSY;
3443                                        goto out_unlock;
3444                                }
3445                        }
3446                }
3447        }
3448
3449        if (!enable && !disable) {
3450                ret = 0;
3451                goto out_unlock;
3452        }
3453
3454        /*
3455         * Except for the root, subtree_control must be zero for a cgroup
3456         * with tasks so that child cgroups don't compete against tasks.
3457         */
3458        if (enable && cgroup_parent(cgrp)) {
3459                struct cgrp_cset_link *link;
3460
3461                /*
3462                 * Because namespaces pin csets too, @cgrp->cset_links
3463                 * might not be empty even when @cgrp is empty.  Walk and
3464                 * verify each cset.
3465                 */
3466                spin_lock_irq(&css_set_lock);
3467
3468                ret = 0;
3469                list_for_each_entry(link, &cgrp->cset_links, cset_link) {
3470                        if (css_set_populated(link->cset)) {
3471                                ret = -EBUSY;
3472                                break;
3473                        }
3474                }
3475
3476                spin_unlock_irq(&css_set_lock);
3477
3478                if (ret)
3479                        goto out_unlock;
3480        }
3481
3482        /* save and update control masks and prepare csses */
3483        cgroup_save_control(cgrp);
3484
3485        cgrp->subtree_control |= enable;
3486        cgrp->subtree_control &= ~disable;
3487
3488        ret = cgroup_apply_control(cgrp);
3489
3490        cgroup_finalize_control(cgrp, ret);
3491
3492        kernfs_activate(cgrp->kn);
3493        ret = 0;
3494out_unlock:
3495        cgroup_kn_unlock(of->kn);
3496        return ret ?: nbytes;
3497}
3498
3499static int cgroup_events_show(struct seq_file *seq, void *v)
3500{
3501        seq_printf(seq, "populated %d\n",
3502                   cgroup_is_populated(seq_css(seq)->cgroup));
3503        return 0;
3504}
3505
3506static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
3507                                 size_t nbytes, loff_t off)
3508{
3509        struct cgroup *cgrp = of->kn->parent->priv;
3510        struct cftype *cft = of->kn->priv;
3511        struct cgroup_subsys_state *css;
3512        int ret;
3513
3514        if (cft->write)
3515                return cft->write(of, buf, nbytes, off);
3516
3517        /*
3518         * kernfs guarantees that a file isn't deleted with operations in
3519         * flight, which means that the matching css is and stays alive and
3520         * doesn't need to be pinned.  The RCU locking is not necessary
3521         * either.  It's just for the convenience of using cgroup_css().
3522         */
3523        rcu_read_lock();
3524        css = cgroup_css(cgrp, cft->ss);
3525        rcu_read_unlock();
3526
3527        if (cft->write_u64) {
3528                unsigned long long v;
3529                ret = kstrtoull(buf, 0, &v);
3530                if (!ret)
3531                        ret = cft->write_u64(css, cft, v);
3532        } else if (cft->write_s64) {
3533                long long v;
3534                ret = kstrtoll(buf, 0, &v);
3535                if (!ret)
3536                        ret = cft->write_s64(css, cft, v);
3537        } else {
3538                ret = -EINVAL;
3539        }
3540
3541        return ret ?: nbytes;
3542}
3543
3544static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos)
3545{
3546        return seq_cft(seq)->seq_start(seq, ppos);
3547}
3548
3549static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos)
3550{
3551        return seq_cft(seq)->seq_next(seq, v, ppos);
3552}
3553
3554static void cgroup_seqfile_stop(struct seq_file *seq, void *v)
3555{
3556        seq_cft(seq)->seq_stop(seq, v);
3557}
3558
3559static int cgroup_seqfile_show(struct seq_file *m, void *arg)
3560{
3561        struct cftype *cft = seq_cft(m);
3562        struct cgroup_subsys_state *css = seq_css(m);
3563
3564        if (cft->seq_show)
3565                return cft->seq_show(m, arg);
3566
3567        if (cft->read_u64)
3568                seq_printf(m, "%llu\n", cft->read_u64(css, cft));
3569        else if (cft->read_s64)
3570                seq_printf(m, "%lld\n", cft->read_s64(css, cft));
3571        else
3572                return -EINVAL;
3573        return 0;
3574}
3575
3576static struct kernfs_ops cgroup_kf_single_ops = {
3577        .atomic_write_len       = PAGE_SIZE,
3578        .write                  = cgroup_file_write,
3579        .seq_show               = cgroup_seqfile_show,
3580};
3581
3582static struct kernfs_ops cgroup_kf_ops = {
3583        .atomic_write_len       = PAGE_SIZE,
3584        .write                  = cgroup_file_write,
3585        .seq_start              = cgroup_seqfile_start,
3586        .seq_next               = cgroup_seqfile_next,
3587        .seq_stop               = cgroup_seqfile_stop,
3588        .seq_show               = cgroup_seqfile_show,
3589};
3590
3591/*
3592 * cgroup_rename - Only allow simple rename of directories in place.
3593 */
3594static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
3595                         const char *new_name_str)
3596{
3597        struct cgroup *cgrp = kn->priv;
3598        int ret;
3599
3600        if (kernfs_type(kn) != KERNFS_DIR)
3601                return -ENOTDIR;
3602        if (kn->parent != new_parent)
3603                return -EIO;
3604
3605        /*
3606         * This isn't a proper migration and its usefulness is very
3607         * limited.  Disallow on the default hierarchy.
3608         */
3609        if (cgroup_on_dfl(cgrp))
3610                return -EPERM;
3611
3612        /*
3613         * We're gonna grab cgroup_mutex which nests outside kernfs
3614         * active_ref.  kernfs_rename() doesn't require active_ref
3615         * protection.  Break them before grabbing cgroup_mutex.
3616         */
3617        kernfs_break_active_protection(new_parent);
3618        kernfs_break_active_protection(kn);
3619
3620        mutex_lock(&cgroup_mutex);
3621
3622        ret = kernfs_rename(kn, new_parent, new_name_str);
3623        if (!ret)
3624                trace_cgroup_rename(cgrp);
3625
3626        mutex_unlock(&cgroup_mutex);
3627
3628        kernfs_unbreak_active_protection(kn);
3629        kernfs_unbreak_active_protection(new_parent);
3630        return ret;
3631}
3632
3633/* set uid and gid of cgroup dirs and files to that of the creator */
3634static int cgroup_kn_set_ugid(struct kernfs_node *kn)
3635{
3636        struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
3637                               .ia_uid = current_fsuid(),
3638                               .ia_gid = current_fsgid(), };
3639
3640        if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
3641            gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
3642                return 0;
3643
3644        return kernfs_setattr(kn, &iattr);
3645}
3646
3647static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
3648                           struct cftype *cft)
3649{
3650        char name[CGROUP_FILE_NAME_MAX];
3651        struct kernfs_node *kn;
3652        struct lock_class_key *key = NULL;
3653        int ret;
3654
3655#ifdef CONFIG_DEBUG_LOCK_ALLOC
3656        key = &cft->lockdep_key;
3657#endif
3658        kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name),
3659                                  cgroup_file_mode(cft), 0, cft->kf_ops, cft,
3660                                  NULL, key);
3661        if (IS_ERR(kn))
3662                return PTR_ERR(kn);
3663
3664        ret = cgroup_kn_set_ugid(kn);
3665        if (ret) {
3666                kernfs_remove(kn);
3667                return ret;
3668        }
3669
3670        if (cft->file_offset) {
3671                struct cgroup_file *cfile = (void *)css + cft->file_offset;
3672
3673                spin_lock_irq(&cgroup_file_kn_lock);
3674                cfile->kn = kn;
3675                spin_unlock_irq(&cgroup_file_kn_lock);
3676        }
3677
3678        return 0;
3679}
3680
3681/**
3682 * cgroup_addrm_files - add or remove files to a cgroup directory
3683 * @css: the target css
3684 * @cgrp: the target cgroup (usually css->cgroup)
3685 * @cfts: array of cftypes to be added
3686 * @is_add: whether to add or remove
3687 *
3688 * Depending on @is_add, add or remove files defined by @cfts on @cgrp.
3689 * For removals, this function never fails.
3690 */
3691static int cgroup_addrm_files(struct cgroup_subsys_state *css,
3692                              struct cgroup *cgrp, struct cftype cfts[],
3693                              bool is_add)
3694{
3695        struct cftype *cft, *cft_end = NULL;
3696        int ret = 0;
3697
3698        lockdep_assert_held(&cgroup_mutex);
3699
3700restart:
3701        for (cft = cfts; cft != cft_end && cft->name[0] != '\0'; cft++) {
3702                /* does cft->flags tell us to skip this file on @cgrp? */
3703                if ((cft->flags & __CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
3704                        continue;
3705                if ((cft->flags & __CFTYPE_NOT_ON_DFL) && cgroup_on_dfl(cgrp))
3706                        continue;
3707                if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
3708                        continue;
3709                if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgroup_parent(cgrp))
3710                        continue;
3711
3712                if (is_add) {
3713                        ret = cgroup_add_file(css, cgrp, cft);
3714                        if (ret) {
3715                                pr_warn("%s: failed to add %s, err=%d\n",
3716                                        __func__, cft->name, ret);
3717                                cft_end = cft;
3718                                is_add = false;
3719                                goto restart;
3720                        }
3721                } else {
3722                        cgroup_rm_file(cgrp, cft);
3723                }
3724        }
3725        return ret;
3726}
3727
3728static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add)
3729{
3730        LIST_HEAD(pending);
3731        struct cgroup_subsys *ss = cfts[0].ss;
3732        struct cgroup *root = &ss->root->cgrp;
3733        struct cgroup_subsys_state *css;
3734        int ret = 0;
3735
3736        lockdep_assert_held(&cgroup_mutex);
3737
3738        /* add/rm files for all cgroups created before */
3739        css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
3740                struct cgroup *cgrp = css->cgroup;
3741
3742                if (!(css->flags & CSS_VISIBLE))
3743                        continue;
3744
3745                ret = cgroup_addrm_files(css, cgrp, cfts, is_add);
3746                if (ret)
3747                        break;
3748        }
3749
3750        if (is_add && !ret)
3751                kernfs_activate(root->kn);
3752        return ret;
3753}
3754
3755static void cgroup_exit_cftypes(struct cftype *cfts)
3756{
3757        struct cftype *cft;
3758
3759        for (cft = cfts; cft->name[0] != '\0'; cft++) {
3760                /* free copy for custom atomic_write_len, see init_cftypes() */
3761                if (cft->max_write_len && cft->max_write_len != PAGE_SIZE)
3762                        kfree(cft->kf_ops);
3763                cft->kf_ops = NULL;
3764                cft->ss = NULL;
3765
3766                /* revert flags set by cgroup core while adding @cfts */
3767                cft->flags &= ~(__CFTYPE_ONLY_ON_DFL | __CFTYPE_NOT_ON_DFL);
3768        }
3769}
3770
3771static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3772{
3773        struct cftype *cft;
3774
3775        for (cft = cfts; cft->name[0] != '\0'; cft++) {
3776                struct kernfs_ops *kf_ops;
3777
3778                WARN_ON(cft->ss || cft->kf_ops);
3779
3780                if (cft->seq_start)
3781                        kf_ops = &cgroup_kf_ops;
3782                else
3783                        kf_ops = &cgroup_kf_single_ops;
3784
3785                /*
3786                 * Ugh... if @cft wants a custom max_write_len, we need to
3787                 * make a copy of kf_ops to set its atomic_write_len.
3788                 */
3789                if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) {
3790                        kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL);
3791                        if (!kf_ops) {
3792                                cgroup_exit_cftypes(cfts);
3793                                return -ENOMEM;
3794                        }
3795                        kf_ops->atomic_write_len = cft->max_write_len;
3796                }
3797
3798                cft->kf_ops = kf_ops;
3799                cft->ss = ss;
3800        }
3801
3802        return 0;
3803}
3804
3805static int cgroup_rm_cftypes_locked(struct cftype *cfts)
3806{
3807        lockdep_assert_held(&cgroup_mutex);
3808
3809        if (!cfts || !cfts[0].ss)
3810                return -ENOENT;
3811
3812        list_del(&cfts->node);
3813        cgroup_apply_cftypes(cfts, false);
3814        cgroup_exit_cftypes(cfts);
3815        return 0;
3816}
3817
3818/**
3819 * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
3820 * @cfts: zero-length name terminated array of cftypes
3821 *
3822 * Unregister @cfts.  Files described by @cfts are removed from all
3823 * existing cgroups and all future cgroups won't have them either.  This
3824 * function can be called anytime whether @cfts' subsys is attached or not.
3825 *
3826 * Returns 0 on successful unregistration, -ENOENT if @cfts is not
3827 * registered.
3828 */
3829int cgroup_rm_cftypes(struct cftype *cfts)
3830{
3831        int ret;
3832
3833        mutex_lock(&cgroup_mutex);
3834        ret = cgroup_rm_cftypes_locked(cfts);
3835        mutex_unlock(&cgroup_mutex);
3836        return ret;
3837}
3838
3839/**
3840 * cgroup_add_cftypes - add an array of cftypes to a subsystem
3841 * @ss: target cgroup subsystem
3842 * @cfts: zero-length name terminated array of cftypes
3843 *
3844 * Register @cfts to @ss.  Files described by @cfts are created for all
3845 * existing cgroups to which @ss is attached and all future cgroups will
3846 * have them too.  This function can be called anytime whether @ss is
3847 * attached or not.
3848 *
3849 * Returns 0 on successful registration, -errno on failure.  Note that this
3850 * function currently returns 0 as long as @cfts registration is successful
3851 * even if some file creation attempts on existing cgroups fail.
3852 */
3853static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3854{
3855        int ret;
3856
3857        if (!cgroup_ssid_enabled(ss->id))
3858                return 0;
3859
3860        if (!cfts || cfts[0].name[0] == '\0')
3861                return 0;
3862
3863        ret = cgroup_init_cftypes(ss, cfts);
3864        if (ret)
3865                return ret;
3866
3867        mutex_lock(&cgroup_mutex);
3868
3869        list_add_tail(&cfts->node, &ss->cfts);
3870        ret = cgroup_apply_cftypes(cfts, true);
3871        if (ret)
3872                cgroup_rm_cftypes_locked(cfts);
3873
3874        mutex_unlock(&cgroup_mutex);
3875        return ret;
3876}
3877
3878/**
3879 * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
3880 * @ss: target cgroup subsystem
3881 * @cfts: zero-length name terminated array of cftypes
3882 *
3883 * Similar to cgroup_add_cftypes() but the added files are only used for
3884 * the default hierarchy.
3885 */
3886int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3887{
3888        struct cftype *cft;
3889
3890        for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3891                cft->flags |= __CFTYPE_ONLY_ON_DFL;
3892        return cgroup_add_cftypes(ss, cfts);
3893}
3894
3895/**
3896 * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
3897 * @ss: target cgroup subsystem
3898 * @cfts: zero-length name terminated array of cftypes
3899 *
3900 * Similar to cgroup_add_cftypes() but the added files are only used for
3901 * the legacy hierarchies.
3902 */
3903int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
3904{
3905        struct cftype *cft;
3906
3907        for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
3908                cft->flags |= __CFTYPE_NOT_ON_DFL;
3909        return cgroup_add_cftypes(ss, cfts);
3910}
3911
3912/**
3913 * cgroup_file_notify - generate a file modified event for a cgroup_file
3914 * @cfile: target cgroup_file
3915 *
3916 * @cfile must have been obtained by setting cftype->file_offset.
3917 */
3918void cgroup_file_notify(struct cgroup_file *cfile)
3919{
3920        unsigned long flags;
3921
3922        spin_lock_irqsave(&cgroup_file_kn_lock, flags);
3923        if (cfile->kn)
3924                kernfs_notify(cfile->kn);
3925        spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
3926}
3927
3928/**
3929 * cgroup_task_count - count the number of tasks in a cgroup.
3930 * @cgrp: the cgroup in question
3931 *
3932 * Return the number of tasks in the cgroup.  The returned number can be
3933 * higher than the actual number of tasks due to css_set references from
3934 * namespace roots and temporary usages.
3935 */
3936static int cgroup_task_count(const struct cgroup *cgrp)
3937{
3938        int count = 0;
3939        struct cgrp_cset_link *link;
3940
3941        spin_lock_irq(&css_set_lock);
3942        list_for_each_entry(link, &cgrp->cset_links, cset_link)
3943                count += atomic_read(&link->cset->refcount);
3944        spin_unlock_irq(&css_set_lock);
3945        return count;
3946}
3947
3948/**
3949 * css_next_child - find the next child of a given css
3950 * @pos: the current position (%NULL to initiate traversal)
3951 * @parent: css whose children to walk
3952 *
3953 * This function returns the next child of @parent and should be called
3954 * under either cgroup_mutex or RCU read lock.  The only requirement is
3955 * that @parent and @pos are accessible.  The next sibling is guaranteed to
3956 * be returned regardless of their states.
3957 *
3958 * If a subsystem synchronizes ->css_online() and the start of iteration, a
3959 * css which finished ->css_online() is guaranteed to be visible in the
3960 * future iterations and will stay visible until the last reference is put.
3961 * A css which hasn't finished ->css_online() or already finished
3962 * ->css_offline() may show up during traversal.  It's each subsystem's
3963 * responsibility to synchronize against on/offlining.
3964 */
3965struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
3966                                           struct cgroup_subsys_state *parent)
3967{
3968        struct cgroup_subsys_state *next;
3969
3970        cgroup_assert_mutex_or_rcu_locked();
3971
3972        /*
3973         * @pos could already have been unlinked from the sibling list.
3974         * Once a cgroup is removed, its ->sibling.next is no longer
3975         * updated when its next sibling changes.  CSS_RELEASED is set when
3976         * @pos is taken off list, at which time its next pointer is valid,
3977         * and, as releases are serialized, the one pointed to by the next
3978         * pointer is guaranteed to not have started release yet.  This
3979         * implies that if we observe !CSS_RELEASED on @pos in this RCU
3980         * critical section, the one pointed to by its next pointer is
3981         * guaranteed to not have finished its RCU grace period even if we
3982         * have dropped rcu_read_lock() inbetween iterations.
3983         *
3984         * If @pos has CSS_RELEASED set, its next pointer can't be
3985         * dereferenced; however, as each css is given a monotonically
3986         * increasing unique serial number and always appended to the
3987         * sibling list, the next one can be found by walking the parent's
3988         * children until the first css with higher serial number than
3989         * @pos's.  While this path can be slower, it happens iff iteration
3990         * races against release and the race window is very small.
3991         */
3992        if (!pos) {
3993                next = list_entry_rcu(parent->children.next, struct cgroup_subsys_state, sibling);
3994        } else if (likely(!(pos->flags & CSS_RELEASED))) {
3995                next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
3996        } else {
3997                list_for_each_entry_rcu(next, &parent->children, sibling)
3998                        if (next->serial_nr > pos->serial_nr)
3999                                break;
4000        }
4001
4002        /*
4003         * @next, if not pointing to the head, can be dereferenced and is
4004         * the next sibling.
4005         */
4006        if (&next->sibling != &parent->children)
4007                return next;
4008        return NULL;
4009}
4010
4011/**
4012 * css_next_descendant_pre - find the next descendant for pre-order walk
4013 * @pos: the current position (%NULL to initiate traversal)
4014 * @root: css whose descendants to walk
4015 *
4016 * To be used by css_for_each_descendant_pre().  Find the next descendant
4017 * to visit for pre-order traversal of @root's descendants.  @root is
4018 * included in the iteration and the first node to be visited.
4019 *
4020 * While this function requires cgroup_mutex or RCU read locking, it
4021 * doesn't require the whole traversal to be contained in a single critical
4022 * section.  This function will return the correct next descendant as long
4023 * as both @pos and @root are accessible and @pos is a descendant of @root.
4024 *
4025 * If a subsystem synchronizes ->css_online() and the start of iteration, a
4026 * css which finished ->css_online() is guaranteed to be visible in the
4027 * future iterations and will stay visible until the last reference is put.
4028 * A css which hasn't finished ->css_online() or already finished
4029 * ->css_offline() may show up during traversal.  It's each subsystem's
4030 * responsibility to synchronize against on/offlining.
4031 */
4032struct cgroup_subsys_state *
4033css_next_descendant_pre(struct cgroup_subsys_state *pos,
4034                        struct cgroup_subsys_state *root)
4035{
4036        struct cgroup_subsys_state *next;
4037
4038        cgroup_assert_mutex_or_rcu_locked();
4039
4040        /* if first iteration, visit @root */
4041        if (!pos)
4042                return root;
4043
4044        /* visit the first child if exists */
4045        next = css_next_child(NULL, pos);
4046        if (next)
4047                return next;
4048
4049        /* no child, visit my or the closest ancestor's next sibling */
4050        while (pos != root) {
4051                next = css_next_child(pos, pos->parent);
4052                if (next)
4053                        return next;
4054                pos = pos->parent;
4055        }
4056
4057        return NULL;
4058}
4059
4060/**
4061 * css_rightmost_descendant - return the rightmost descendant of a css
4062 * @pos: css of interest
4063 *
4064 * Return the rightmost descendant of @pos.  If there's no descendant, @pos
4065 * is returned.  This can be used during pre-order traversal to skip
4066 * subtree of @pos.
4067 *
4068 * While this function requires cgroup_mutex or RCU read locking, it
4069 * doesn't require the whole traversal to be contained in a single critical
4070 * section.  This function will return the correct rightmost descendant as
4071 * long as @pos is accessible.
4072 */
4073struct cgroup_subsys_state *
4074css_rightmost_descendant(struct cgroup_subsys_state *pos)
4075{
4076        struct cgroup_subsys_state *last, *tmp;
4077
4078        cgroup_assert_mutex_or_rcu_locked();
4079
4080        do {
4081                last = pos;
4082                /* ->prev isn't RCU safe, walk ->next till the end */
4083                pos = NULL;
4084                css_for_each_child(tmp, last)
4085                        pos = tmp;
4086        } while (pos);
4087
4088        return last;
4089}
4090
4091static struct cgroup_subsys_state *
4092css_leftmost_descendant(struct cgroup_subsys_state *pos)
4093{
4094        struct cgroup_subsys_state *last;
4095
4096        do {
4097                last = pos;
4098                pos = css_next_child(NULL, pos);
4099        } while (pos);
4100
4101        return last;
4102}
4103
4104/**
4105 * css_next_descendant_post - find the next descendant for post-order walk
4106 * @pos: the current position (%NULL to initiate traversal)
4107 * @root: css whose descendants to walk
4108 *
4109 * To be used by css_for_each_descendant_post().  Find the next descendant
4110 * to visit for post-order traversal of @root's descendants.  @root is
4111 * included in the iteration and the last node to be visited.
4112 *
4113 * While this function requires cgroup_mutex or RCU read locking, it
4114 * doesn't require the whole traversal to be contained in a single critical
4115 * section.  This function will return the correct next descendant as long
4116 * as both @pos and @cgroup are accessible and @pos is a descendant of
4117 * @cgroup.
4118 *
4119 * If a subsystem synchronizes ->css_online() and the start of iteration, a
4120 * css which finished ->css_online() is guaranteed to be visible in the
4121 * future iterations and will stay visible until the last reference is put.
4122 * A css which hasn't finished ->css_online() or already finished
4123 * ->css_offline() may show up during traversal.  It's each subsystem's
4124 * responsibility to synchronize against on/offlining.
4125 */
4126struct cgroup_subsys_state *
4127css_next_descendant_post(struct cgroup_subsys_state *pos,
4128                         struct cgroup_subsys_state *root)
4129{
4130        struct cgroup_subsys_state *next;
4131
4132        cgroup_assert_mutex_or_rcu_locked();
4133
4134        /* if first iteration, visit leftmost descendant which may be @root */
4135        if (!pos)
4136                return css_leftmost_descendant(root);
4137
4138        /* if we visited @root, we're done */
4139        if (pos == root)
4140                return NULL;
4141
4142        /* if there's an unvisited sibling, visit its leftmost descendant */
4143        next = css_next_child(pos, pos->parent);
4144        if (next)
4145                return css_leftmost_descendant(next);
4146
4147        /* no sibling left, visit parent */
4148        return pos->parent;
4149}
4150
4151/**
4152 * css_has_online_children - does a css have online children
4153 * @css: the target css
4154 *
4155 * Returns %true if @css has any online children; otherwise, %false.  This
4156 * function can be called from any context but the caller is responsible
4157 * for synchronizing against on/offlining as necessary.
4158 */
4159bool css_has_online_children(struct cgroup_subsys_state *css)
4160{
4161        struct cgroup_subsys_state *child;
4162        bool ret = false;
4163
4164        rcu_read_lock();
4165        css_for_each_child(child, css) {
4166                if (child->flags & CSS_ONLINE) {
4167                        ret = true;
4168                        break;
4169                }
4170        }
4171        rcu_read_unlock();
4172        return ret;
4173}
4174
4175/**
4176 * css_task_iter_advance_css_set - advance a task itererator to the next css_set
4177 * @it: the iterator to advance
4178 *
4179 * Advance @it to the next css_set to walk.
4180 */
4181static void css_task_iter_advance_css_set(struct css_task_iter *it)
4182{
4183        struct list_head *l = it->cset_pos;
4184        struct cgrp_cset_link *link;
4185        struct css_set *cset;
4186
4187        lockdep_assert_held(&css_set_lock);
4188
4189        /* Advance to the next non-empty css_set */
4190        do {
4191                l = l->next;
4192                if (l == it->cset_head) {
4193                        it->cset_pos = NULL;
4194                        it->task_pos = NULL;
4195                        return;
4196                }
4197
4198                if (it->ss) {
4199                        cset = container_of(l, struct css_set,
4200                                            e_cset_node[it->ss->id]);
4201                } else {
4202                        link = list_entry(l, struct cgrp_cset_link, cset_link);
4203                        cset = link->cset;
4204                }
4205        } while (!css_set_populated(cset));
4206
4207        it->cset_pos = l;
4208
4209        if (!list_empty(&cset->tasks))
4210                it->task_pos = cset->tasks.next;
4211        else
4212                it->task_pos = cset->mg_tasks.next;
4213
4214        it->tasks_head = &cset->tasks;
4215        it->mg_tasks_head = &cset->mg_tasks;
4216
4217        /*
4218         * We don't keep css_sets locked across iteration steps and thus
4219         * need to take steps to ensure that iteration can be resumed after
4220         * the lock is re-acquired.  Iteration is performed at two levels -
4221         * css_sets and tasks in them.
4222         *
4223         * Once created, a css_set never leaves its cgroup lists, so a
4224         * pinned css_set is guaranteed to stay put and we can resume
4225         * iteration afterwards.
4226         *
4227         * Tasks may leave @cset across iteration steps.  This is resolved
4228         * by registering each iterator with the css_set currently being
4229         * walked and making css_set_move_task() advance iterators whose
4230         * next task is leaving.
4231         */
4232        if (it->cur_cset) {
4233                list_del(&it->iters_node);
4234                put_css_set_locked(it->cur_cset);
4235        }
4236        get_css_set(cset);
4237        it->cur_cset = cset;
4238        list_add(&it->iters_node, &cset->task_iters);
4239}
4240
4241static void css_task_iter_advance(struct css_task_iter *it)
4242{
4243        struct list_head *l = it->task_pos;
4244
4245        lockdep_assert_held(&css_set_lock);
4246        WARN_ON_ONCE(!l);
4247
4248        /*
4249         * Advance iterator to find next entry.  cset->tasks is consumed
4250         * first and then ->mg_tasks.  After ->mg_tasks, we move onto the
4251         * next cset.
4252         */
4253        l = l->next;
4254
4255        if (l == it->tasks_head)
4256                l = it->mg_tasks_head->next;
4257
4258        if (l == it->mg_tasks_head)
4259                css_task_iter_advance_css_set(it);
4260        else
4261                it->task_pos = l;
4262}
4263
4264/**
4265 * css_task_iter_start - initiate task iteration
4266 * @css: the css to walk tasks of
4267 * @it: the task iterator to use
4268 *
4269 * Initiate iteration through the tasks of @css.  The caller can call
4270 * css_task_iter_next() to walk through the tasks until the function
4271 * returns NULL.  On completion of iteration, css_task_iter_end() must be
4272 * called.
4273 */
4274void css_task_iter_start(struct cgroup_subsys_state *css,
4275                         struct css_task_iter *it)
4276{
4277        /* no one should try to iterate before mounting cgroups */
4278        WARN_ON_ONCE(!use_task_css_set_links);
4279
4280        memset(it, 0, sizeof(*it));
4281
4282        spin_lock_irq(&css_set_lock);
4283
4284        it->ss = css->ss;
4285
4286        if (it->ss)
4287                it->cset_pos = &css->cgroup->e_csets[css->ss->id];
4288        else
4289                it->cset_pos = &css->cgroup->cset_links;
4290
4291        it->cset_head = it->cset_pos;
4292
4293        css_task_iter_advance_css_set(it);
4294
4295        spin_unlock_irq(&css_set_lock);
4296}
4297
4298/**
4299 * css_task_iter_next - return the next task for the iterator
4300 * @it: the task iterator being iterated
4301 *
4302 * The "next" function for task iteration.  @it should have been
4303 * initialized via css_task_iter_start().  Returns NULL when the iteration
4304 * reaches the end.
4305 */
4306struct task_struct *css_task_iter_next(struct css_task_iter *it)
4307{
4308        if (it->cur_task) {
4309                put_task_struct(it->cur_task);
4310                it->cur_task = NULL;
4311        }
4312
4313        spin_lock_irq(&css_set_lock);
4314
4315        if (it->task_pos) {
4316                it->cur_task = list_entry(it->task_pos, struct task_struct,
4317                                          cg_list);
4318                get_task_struct(it->cur_task);
4319                css_task_iter_advance(it);
4320        }
4321
4322        spin_unlock_irq(&css_set_lock);
4323
4324        return it->cur_task;
4325}
4326
4327/**
4328 * css_task_iter_end - finish task iteration
4329 * @it: the task iterator to finish
4330 *
4331 * Finish task iteration started by css_task_iter_start().
4332 */
4333void css_task_iter_end(struct css_task_iter *it)
4334{
4335        if (it->cur_cset) {
4336                spin_lock_irq(&css_set_lock);
4337                list_del(&it->iters_node);
4338                put_css_set_locked(it->cur_cset);
4339                spin_unlock_irq(&css_set_lock);
4340        }
4341
4342        if (it->cur_task)
4343                put_task_struct(it->cur_task);
4344}
4345
4346/**
4347 * cgroup_trasnsfer_tasks - move tasks from one cgroup to another
4348 * @to: cgroup to which the tasks will be moved
4349 * @from: cgroup in which the tasks currently reside
4350 *
4351 * Locking rules between cgroup_post_fork() and the migration path
4352 * guarantee that, if a task is forking while being migrated, the new child
4353 * is guaranteed to be either visible in the source cgroup after the
4354 * parent's migration is complete or put into the target cgroup.  No task
4355 * can slip out of migration through forking.
4356 */
4357int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
4358{
4359        LIST_HEAD(preloaded_csets);
4360        struct cgrp_cset_link *link;
4361        struct css_task_iter it;
4362        struct task_struct *task;
4363        int ret;
4364
4365        if (!cgroup_may_migrate_to(to))
4366                return -EBUSY;
4367
4368        mutex_lock(&cgroup_mutex);
4369
4370        percpu_down_write(&cgroup_threadgroup_rwsem);
4371
4372        /* all tasks in @from are being moved, all csets are source */
4373        spin_lock_irq(&css_set_lock);
4374        list_for_each_entry(link, &from->cset_links, cset_link)
4375                cgroup_migrate_add_src(link->cset, to, &preloaded_csets);
4376        spin_unlock_irq(&css_set_lock);
4377
4378        ret = cgroup_migrate_prepare_dst(&preloaded_csets);
4379        if (ret)
4380                goto out_err;
4381
4382        /*
4383         * Migrate tasks one-by-one until @from is empty.  This fails iff
4384         * ->can_attach() fails.
4385         */
4386        do {
4387                css_task_iter_start(&from->self, &it);
4388                task = css_task_iter_next(&it);
4389                if (task)
4390                        get_task_struct(task);
4391                css_task_iter_end(&it);
4392
4393                if (task) {
4394                        ret = cgroup_migrate(task, false, to->root);
4395                        if (!ret)
4396                                trace_cgroup_transfer_tasks(to, task, false);
4397                        put_task_struct(task);
4398                }
4399        } while (task && !ret);
4400out_err:
4401        cgroup_migrate_finish(&preloaded_csets);
4402        percpu_up_write(&cgroup_threadgroup_rwsem);
4403        mutex_unlock(&cgroup_mutex);
4404        return ret;
4405}
4406
4407/*
4408 * Stuff for reading the 'tasks'/'procs' files.
4409 *
4410 * Reading this file can return large amounts of data if a cgroup has
4411 * *lots* of attached tasks. So it may need several calls to read(),
4412 * but we cannot guarantee that the information we produce is correct
4413 * unless we produce it entirely atomically.
4414 *
4415 */
4416
4417/* which pidlist file are we talking about? */
4418enum cgroup_filetype {
4419        CGROUP_FILE_PROCS,
4420        CGROUP_FILE_TASKS,
4421};
4422
4423/*
4424 * A pidlist is a list of pids that virtually represents the contents of one
4425 * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists,
4426 * a pair (one each for procs, tasks) for each pid namespace that's relevant
4427 * to the cgroup.
4428 */
4429struct cgroup_pidlist {
4430        /*
4431         * used to find which pidlist is wanted. doesn't change as long as
4432         * this particular list stays in the list.
4433        */
4434        struct { enum cgroup_filetype type; struct pid_namespace *ns; } key;
4435        /* array of xids */
4436        pid_t *list;
4437        /* how many elements the above list has */
4438        int length;
4439        /* each of these stored in a list by its cgroup */
4440        struct list_head links;
4441        /* pointer to the cgroup we belong to, for list removal purposes */
4442        struct cgroup *owner;
4443        /* for delayed destruction */
4444        struct delayed_work destroy_dwork;
4445};
4446
4447/*
4448 * The following two functions "fix" the issue where there are more pids
4449 * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
4450 * TODO: replace with a kernel-wide solution to this problem
4451 */
4452#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
4453static void *pidlist_allocate(int count)
4454{
4455        if (PIDLIST_TOO_LARGE(count))
4456                return vmalloc(count * sizeof(pid_t));
4457        else
4458                return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
4459}
4460
4461static void pidlist_free(void *p)
4462{
4463        kvfree(p);
4464}
4465
4466/*
4467 * Used to destroy all pidlists lingering waiting for destroy timer.  None
4468 * should be left afterwards.
4469 */
4470static void cgroup_pidlist_destroy_all(struct cgroup *cgrp)
4471{
4472        struct cgroup_pidlist *l, *tmp_l;
4473
4474        mutex_lock(&cgrp->pidlist_mutex);
4475        list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links)
4476                mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0);
4477        mutex_unlock(&cgrp->pidlist_mutex);
4478
4479        flush_workqueue(cgroup_pidlist_destroy_wq);
4480        BUG_ON(!list_empty(&cgrp->pidlists));
4481}
4482
4483static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
4484{
4485        struct delayed_work *dwork = to_delayed_work(work);
4486        struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist,
4487                                                destroy_dwork);
4488        struct cgroup_pidlist *tofree = NULL;
4489
4490        mutex_lock(&l->owner->pidlist_mutex);
4491
4492        /*
4493         * Destroy iff we didn't get queued again.  The state won't change
4494         * as destroy_dwork can only be queued while locked.
4495         */
4496        if (!delayed_work_pending(dwork)) {
4497                list_del(&l->links);
4498                pidlist_free(l->list);
4499                put_pid_ns(l->key.ns);
4500                tofree = l;
4501        }
4502
4503        mutex_unlock(&l->owner->pidlist_mutex);
4504        kfree(tofree);
4505}
4506
4507/*
4508 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
4509 * Returns the number of unique elements.
4510 */
4511static int pidlist_uniq(pid_t *list, int length)
4512{
4513        int src, dest = 1;
4514
4515        /*
4516         * we presume the 0th element is unique, so i starts at 1. trivial
4517         * edge cases first; no work needs to be done for either
4518         */
4519        if (length == 0 || length == 1)
4520                return length;
4521        /* src and dest walk down the list; dest counts unique elements */
4522        for (src = 1; src < length; src++) {
4523                /* find next unique element */
4524                while (list[src] == list[src-1]) {
4525                        src++;
4526                        if (src == length)
4527                                goto after;
4528                }
4529                /* dest always points to where the next unique element goes */
4530                list[dest] = list[src];
4531                dest++;
4532        }
4533after:
4534        return dest;
4535}
4536
4537/*
4538 * The two pid files - task and cgroup.procs - guaranteed that the result
4539 * is sorted, which forced this whole pidlist fiasco.  As pid order is
4540 * different per namespace, each namespace needs differently sorted list,
4541 * making it impossible to use, for example, single rbtree of member tasks
4542 * sorted by task pointer.  As pidlists can be fairly large, allocating one
4543 * per open file is dangerous, so cgroup had to implement shared pool of
4544 * pidlists keyed by cgroup and namespace.
4545 *
4546 * All this extra complexity was caused by the original implementation
4547 * committing to an entirely unnecessary property.  In the long term, we
4548 * want to do away with it.  Explicitly scramble sort order if on the
4549 * default hierarchy so that no such expectation exists in the new
4550 * interface.
4551 *
4552 * Scrambling is done by swapping every two consecutive bits, which is
4553 * non-identity one-to-one mapping which disturbs sort order sufficiently.
4554 */
4555static pid_t pid_fry(pid_t pid)
4556{
4557        unsigned a = pid & 0x55555555;
4558        unsigned b = pid & 0xAAAAAAAA;
4559
4560        return (a << 1) | (b >> 1);
4561}
4562
4563static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
4564{
4565        if (cgroup_on_dfl(cgrp))
4566                return pid_fry(pid);
4567        else
4568                return pid;
4569}
4570
4571static int cmppid(const void *a, const void *b)
4572{
4573        return *(pid_t *)a - *(pid_t *)b;
4574}
4575
4576static int fried_cmppid(const void *a, const void *b)
4577{
4578        return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b);
4579}
4580
4581static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
4582                                                  enum cgroup_filetype type)
4583{
4584        struct cgroup_pidlist *l;
4585        /* don't need task_nsproxy() if we're looking at ourself */
4586        struct pid_namespace *ns = task_active_pid_ns(current);
4587
4588        lockdep_assert_held(&cgrp->pidlist_mutex);
4589
4590        list_for_each_entry(l, &cgrp->pidlists, links)
4591                if (l->key.type == type && l->key.ns == ns)
4592                        return l;
4593        return NULL;
4594}
4595
4596/*
4597 * find the appropriate pidlist for our purpose (given procs vs tasks)
4598 * returns with the lock on that pidlist already held, and takes care
4599 * of the use count, or returns NULL with no locks held if we're out of
4600 * memory.
4601 */
4602static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
4603                                                enum cgroup_filetype type)
4604{
4605        struct cgroup_pidlist *l;
4606
4607        lockdep_assert_held(&cgrp->pidlist_mutex);
4608
4609        l = cgroup_pidlist_find(cgrp, type);
4610        if (l)
4611                return l;
4612
4613        /* entry not found; create a new one */
4614        l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
4615        if (!l)
4616                return l;
4617
4618        INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn);
4619        l->key.type = type;
4620        /* don't need task_nsproxy() if we're looking at ourself */
4621        l->key.ns = get_pid_ns(task_active_pid_ns(current));
4622        l->owner = cgrp;
4623        list_add(&l->links, &cgrp->pidlists);
4624        return l;
4625}
4626
4627/*
4628 * Load a cgroup's pidarray with either procs' tgids or tasks' pids
4629 */
4630static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
4631                              struct cgroup_pidlist **lp)
4632{
4633        pid_t *array;
4634        int length;
4635        int pid, n = 0; /* used for populating the array */
4636        struct css_task_iter it;
4637        struct task_struct *tsk;
4638        struct cgroup_pidlist *l;
4639
4640        lockdep_assert_held(&cgrp->pidlist_mutex);
4641
4642        /*
4643         * If cgroup gets more users after we read count, we won't have
4644         * enough space - tough.  This race is indistinguishable to the
4645         * caller from the case that the additional cgroup users didn't
4646         * show up until sometime later on.
4647         */
4648        length = cgroup_task_count(cgrp);
4649        array = pidlist_allocate(length);
4650        if (!array)
4651                return -ENOMEM;
4652        /* now, populate the array */
4653        css_task_iter_start(&cgrp->self, &it);
4654        while ((tsk = css_task_iter_next(&it))) {
4655                if (unlikely(n == length))
4656                        break;
4657                /* get tgid or pid for procs or tasks file respectively */
4658                if (type == CGROUP_FILE_PROCS)
4659                        pid = task_tgid_vnr(tsk);
4660                else
4661                        pid = task_pid_vnr(tsk);
4662                if (pid > 0) /* make sure to only use valid results */
4663                        array[n++] = pid;
4664        }
4665        css_task_iter_end(&it);
4666        length = n;
4667        /* now sort & (if procs) strip out duplicates */
4668        if (cgroup_on_dfl(cgrp))
4669                sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
4670        else
4671                sort(array, length, sizeof(pid_t), cmppid, NULL);
4672        if (type == CGROUP_FILE_PROCS)
4673                length = pidlist_uniq(array, length);
4674
4675        l = cgroup_pidlist_find_create(cgrp, type);
4676        if (!l) {
4677                pidlist_free(array);
4678                return -ENOMEM;
4679        }
4680
4681        /* store array, freeing old if necessary */
4682        pidlist_free(l->list);
4683        l->list = array;
4684        l->length = length;
4685        *lp = l;
4686        return 0;
4687}
4688
4689/**
4690 * cgroupstats_build - build and fill cgroupstats
4691 * @stats: cgroupstats to fill information into
4692 * @dentry: A dentry entry belonging to the cgroup for which stats have
4693 * been requested.
4694 *
4695 * Build and fill cgroupstats so that taskstats can export it to user
4696 * space.
4697 */
4698int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
4699{
4700        struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
4701        struct cgroup *cgrp;
4702        struct css_task_iter it;
4703        struct task_struct *tsk;
4704
4705        /* it should be kernfs_node belonging to cgroupfs and is a directory */
4706        if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
4707            kernfs_type(kn) != KERNFS_DIR)
4708                return -EINVAL;
4709
4710        mutex_lock(&cgroup_mutex);
4711
4712        /*
4713         * We aren't being called from kernfs and there's no guarantee on
4714         * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
4715         * @kn->priv is RCU safe.  Let's do the RCU dancing.
4716         */
4717        rcu_read_lock();
4718        cgrp = rcu_dereference(kn->priv);
4719        if (!cgrp || cgroup_is_dead(cgrp)) {
4720                rcu_read_unlock();
4721                mutex_unlock(&cgroup_mutex);
4722                return -ENOENT;
4723        }
4724        rcu_read_unlock();
4725
4726        css_task_iter_start(&cgrp->self, &it);
4727        while ((tsk = css_task_iter_next(&it))) {
4728                switch (tsk->state) {
4729                case TASK_RUNNING:
4730                        stats->nr_running++;
4731                        break;
4732                case TASK_INTERRUPTIBLE:
4733                        stats->nr_sleeping++;
4734                        break;
4735                case TASK_UNINTERRUPTIBLE:
4736                        stats->nr_uninterruptible++;
4737                        break;
4738                case TASK_STOPPED:
4739                        stats->nr_stopped++;
4740                        break;
4741                default:
4742                        if (delayacct_is_task_waiting_on_io(tsk))
4743                                stats->nr_io_wait++;
4744                        break;
4745                }
4746        }
4747        css_task_iter_end(&it);
4748
4749        mutex_unlock(&cgroup_mutex);
4750        return 0;
4751}
4752
4753
4754/*
4755 * seq_file methods for the tasks/procs files. The seq_file position is the
4756 * next pid to display; the seq_file iterator is a pointer to the pid
4757 * in the cgroup->l->list array.
4758 */
4759
4760static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
4761{
4762        /*
4763         * Initially we receive a position value that corresponds to
4764         * one more than the last pid shown (or 0 on the first call or
4765         * after a seek to the start). Use a binary-search to find the
4766         * next pid to display, if any
4767         */
4768        struct kernfs_open_file *of = s->private;
4769        struct cgroup *cgrp = seq_css(s)->cgroup;
4770        struct cgroup_pidlist *l;
4771        enum cgroup_filetype type = seq_cft(s)->private;
4772        int index = 0, pid = *pos;
4773        int *iter, ret;
4774
4775        mutex_lock(&cgrp->pidlist_mutex);
4776
4777        /*
4778         * !NULL @of->priv indicates that this isn't the first start()
4779         * after open.  If the matching pidlist is around, we can use that.
4780         * Look for it.  Note that @of->priv can't be used directly.  It
4781         * could already have been destroyed.
4782         */
4783        if (of->priv)
4784                of->priv = cgroup_pidlist_find(cgrp, type);
4785
4786        /*
4787         * Either this is the first start() after open or the matching
4788         * pidlist has been destroyed inbetween.  Create a new one.
4789         */
4790        if (!of->priv) {
4791                ret = pidlist_array_load(cgrp, type,
4792                                         (struct cgroup_pidlist **)&of->priv);
4793                if (ret)
4794                        return ERR_PTR(ret);
4795        }
4796        l = of->priv;
4797
4798        if (pid) {
4799                int end = l->length;
4800
4801                while (index < end) {
4802                        int mid = (index + end) / 2;
4803                        if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) {
4804                                index = mid;
4805                                break;
4806                        } else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid)
4807                                index = mid + 1;
4808                        else
4809                                end = mid;
4810                }
4811        }
4812        /* If we're off the end of the array, we're done */
4813        if (index >= l->length)
4814                return NULL;
4815        /* Update the abstract position to be the actual pid that we found */
4816        iter = l->list + index;
4817        *pos = cgroup_pid_fry(cgrp, *iter);
4818        return iter;
4819}
4820
4821static void cgroup_pidlist_stop(struct seq_file *s, void *v)
4822{
4823        struct kernfs_open_file *of = s->private;
4824        struct cgroup_pidlist *l = of->priv;
4825
4826        if (l)
4827                mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
4828                                 CGROUP_PIDLIST_DESTROY_DELAY);
4829        mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex);
4830}
4831
4832static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
4833{
4834        struct kernfs_open_file *of = s->private;
4835        struct cgroup_pidlist *l = of->priv;
4836        pid_t *p = v;
4837        pid_t *end = l->list + l->length;
4838        /*
4839         * Advance to the next pid in the array. If this goes off the
4840         * end, we're done
4841         */
4842        p++;
4843        if (p >= end) {
4844                return NULL;
4845        } else {
4846                *pos = cgroup_pid_fry(seq_css(s)->cgroup, *p);
4847                return p;
4848        }
4849}
4850
4851static int cgroup_pidlist_show(struct seq_file *s, void *v)
4852{
4853        seq_printf(s, "%d\n", *(int *)v);
4854
4855        return 0;
4856}
4857
4858static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css,
4859                                         struct cftype *cft)
4860{
4861        return notify_on_release(css->cgroup);
4862}
4863
4864static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css,
4865                                          struct cftype *cft, u64 val)
4866{
4867        if (val)
4868                set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4869        else
4870                clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags);
4871        return 0;
4872}
4873
4874static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css,
4875                                      struct cftype *cft)
4876{
4877        return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4878}
4879
4880static int cgroup_clone_children_write(struct cgroup_subsys_state *css,
4881                                       struct cftype *cft, u64 val)
4882{
4883        if (val)
4884                set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4885        else
4886                clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags);
4887        return 0;
4888}
4889
4890/* cgroup core interface files for the default hierarchy */
4891static struct cftype cgroup_dfl_base_files[] = {
4892        {
4893                .name = "cgroup.procs",
4894                .file_offset = offsetof(struct cgroup, procs_file),
4895                .seq_start = cgroup_pidlist_start,
4896                .seq_next = cgroup_pidlist_next,
4897                .seq_stop = cgroup_pidlist_stop,
4898                .seq_show = cgroup_pidlist_show,
4899                .private = CGROUP_FILE_PROCS,
4900                .write = cgroup_procs_write,
4901        },
4902        {
4903                .name = "cgroup.controllers",
4904                .seq_show = cgroup_controllers_show,
4905        },
4906        {
4907                .name = "cgroup.subtree_control",
4908                .seq_show = cgroup_subtree_control_show,
4909                .write = cgroup_subtree_control_write,
4910        },
4911        {
4912                .name = "cgroup.events",
4913                .flags = CFTYPE_NOT_ON_ROOT,
4914                .file_offset = offsetof(struct cgroup, events_file),
4915                .seq_show = cgroup_events_show,
4916        },
4917        { }     /* terminate */
4918};
4919
4920/* cgroup core interface files for the legacy hierarchies */
4921static struct cftype cgroup_legacy_base_files[] = {
4922        {
4923                .name = "cgroup.procs",
4924                .seq_start = cgroup_pidlist_start,
4925                .seq_next = cgroup_pidlist_next,
4926                .seq_stop = cgroup_pidlist_stop,
4927                .seq_show = cgroup_pidlist_show,
4928                .private = CGROUP_FILE_PROCS,
4929                .write = cgroup_procs_write,
4930        },
4931        {
4932                .name = "cgroup.clone_children",
4933                .read_u64 = cgroup_clone_children_read,
4934                .write_u64 = cgroup_clone_children_write,
4935        },
4936        {
4937                .name = "cgroup.sane_behavior",
4938                .flags = CFTYPE_ONLY_ON_ROOT,
4939                .seq_show = cgroup_sane_behavior_show,
4940        },
4941        {
4942                .name = "tasks",
4943                .seq_start = cgroup_pidlist_start,
4944                .seq_next = cgroup_pidlist_next,
4945                .seq_stop = cgroup_pidlist_stop,
4946                .seq_show = cgroup_pidlist_show,
4947                .private = CGROUP_FILE_TASKS,
4948                .write = cgroup_tasks_write,
4949        },
4950        {
4951                .name = "notify_on_release",
4952                .read_u64 = cgroup_read_notify_on_release,
4953                .write_u64 = cgroup_write_notify_on_release,
4954        },
4955        {
4956                .name = "release_agent",
4957                .flags = CFTYPE_ONLY_ON_ROOT,
4958                .seq_show = cgroup_release_agent_show,
4959                .write = cgroup_release_agent_write,
4960                .max_write_len = PATH_MAX - 1,
4961        },
4962        { }     /* terminate */
4963};
4964
4965/*
4966 * css destruction is four-stage process.
4967 *
4968 * 1. Destruction starts.  Killing of the percpu_ref is initiated.
4969 *    Implemented in kill_css().
4970 *
4971 * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
4972 *    and thus css_tryget_online() is guaranteed to fail, the css can be
4973 *    offlined by invoking offline_css().  After offlining, the base ref is
4974 *    put.  Implemented in css_killed_work_fn().
4975 *
4976 * 3. When the percpu_ref reaches zero, the only possible remaining
4977 *    accessors are inside RCU read sections.  css_release() schedules the
4978 *    RCU callback.
4979 *
4980 * 4. After the grace period, the css can be freed.  Implemented in
4981 *    css_free_work_fn().
4982 *
4983 * It is actually hairier because both step 2 and 4 require process context
4984 * and thus involve punting to css->destroy_work adding two additional
4985 * steps to the already complex sequence.
4986 */
4987static void css_free_work_fn(struct work_struct *work)
4988{
4989        struct cgroup_subsys_state *css =
4990                container_of(work, struct cgroup_subsys_state, destroy_work);
4991        struct cgroup_subsys *ss = css->ss;
4992        struct cgroup *cgrp = css->cgroup;
4993
4994        percpu_ref_exit(&css->refcnt);
4995
4996        if (ss) {
4997                /* css free path */
4998                struct cgroup_subsys_state *parent = css->parent;
4999                int id = css->id;
5000
5001                ss->css_free(css);
5002                cgroup_idr_remove(&ss->css_idr, id);
5003                cgroup_put(cgrp);
5004
5005                if (parent)
5006                        css_put(parent);
5007        } else {
5008                /* cgroup free path */
5009                atomic_dec(&cgrp->root->nr_cgrps);
5010                cgroup_pidlist_destroy_all(cgrp);
5011                cancel_work_sync(&cgrp->release_agent_work);
5012
5013                if (cgroup_parent(cgrp)) {
5014                        /*
5015                         * We get a ref to the parent, and put the ref when
5016                         * this cgroup is being freed, so it's guaranteed
5017                         * that the parent won't be destroyed before its
5018                         * children.
5019                         */
5020                        cgroup_put(cgroup_parent(cgrp));
5021                        kernfs_put(cgrp->kn);
5022                        kfree(cgrp);
5023                } else {
5024                        /*
5025                         * This is root cgroup's refcnt reaching zero,
5026                         * which indicates that the root should be
5027                         * released.
5028                         */
5029                        cgroup_destroy_root(cgrp->root);
5030                }
5031        }
5032}
5033
5034static void css_free_rcu_fn(struct rcu_head *rcu_head)
5035{
5036        struct cgroup_subsys_state *css =
5037                container_of(rcu_head, struct cgroup_subsys_state, rcu_head);
5038
5039        INIT_WORK(&css->destroy_work, css_free_work_fn);
5040        queue_work(cgroup_destroy_wq, &css->destroy_work);
5041}
5042
5043static void css_release_work_fn(struct work_struct *work)
5044{
5045        struct cgroup_subsys_state *css =
5046                container_of(work, struct cgroup_subsys_state, destroy_work);
5047        struct cgroup_subsys *ss = css->ss;
5048        struct cgroup *cgrp = css->cgroup;
5049
5050        mutex_lock(&cgroup_mutex);
5051
5052        css->flags |= CSS_RELEASED;
5053        list_del_rcu(&css->sibling);
5054
5055        if (ss) {
5056                /* css release path */
5057                cgroup_idr_replace(&ss->css_idr, NULL, css->id);
5058                if (ss->css_released)
5059                        ss->css_released(css);
5060        } else {
5061                /* cgroup release path */
5062                trace_cgroup_release(cgrp);
5063
5064                cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
5065                cgrp->id = -1;
5066
5067                /*
5068                 * There are two control paths which try to determine
5069                 * cgroup from dentry without going through kernfs -
5070                 * cgroupstats_build() and css_tryget_online_from_dir().
5071                 * Those are supported by RCU protecting clearing of
5072                 * cgrp->kn->priv backpointer.
5073                 */
5074                if (cgrp->kn)
5075                        RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
5076                                         NULL);
5077        }
5078
5079        mutex_unlock(&cgroup_mutex);
5080
5081        call_rcu(&css->rcu_head, css_free_rcu_fn);
5082}
5083
5084static void css_release(struct percpu_ref *ref)
5085{
5086        struct cgroup_subsys_state *css =
5087                container_of(ref, struct cgroup_subsys_state, refcnt);
5088
5089        INIT_WORK(&css->destroy_work, css_release_work_fn);
5090        queue_work(cgroup_destroy_wq, &css->destroy_work);
5091}
5092
5093static void init_and_link_css(struct cgroup_subsys_state *css,
5094                              struct cgroup_subsys *ss, struct cgroup *cgrp)
5095{
5096        lockdep_assert_held(&cgroup_mutex);
5097
5098        cgroup_get(cgrp);
5099
5100        memset(css, 0, sizeof(*css));
5101        css->cgroup = cgrp;
5102        css->ss = ss;
5103        css->id = -1;
5104        INIT_LIST_HEAD(&css->sibling);
5105        INIT_LIST_HEAD(&css->children);
5106        css->serial_nr = css_serial_nr_next++;
5107        atomic_set(&css->online_cnt, 0);
5108
5109        if (cgroup_parent(cgrp)) {
5110                css->parent = cgroup_css(cgroup_parent(cgrp), ss);
5111                css_get(css->parent);
5112        }
5113
5114        BUG_ON(cgroup_css(cgrp, ss));
5115}
5116
5117/* invoke ->css_online() on a new CSS and mark it online if successful */
5118static int online_css(struct cgroup_subsys_state *css)
5119{
5120        struct cgroup_subsys *ss = css->ss;
5121        int ret = 0;
5122
5123        lockdep_assert_held(&cgroup_mutex);
5124
5125        if (ss->css_online)
5126                ret = ss->css_online(css);
5127        if (!ret) {
5128                css->flags |= CSS_ONLINE;
5129                rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
5130
5131                atomic_inc(&css->online_cnt);
5132                if (css->parent)
5133                        atomic_inc(&css->parent->online_cnt);
5134        }
5135        return ret;
5136}
5137
5138/* if the CSS is online, invoke ->css_offline() on it and mark it offline */
5139static void offline_css(struct cgroup_subsys_state *css)
5140{
5141        struct cgroup_subsys *ss = css->ss;
5142
5143        lockdep_assert_held(&cgroup_mutex);
5144
5145        if (!(css->flags & CSS_ONLINE))
5146                return;
5147
5148        if (ss->css_reset)
5149                ss->css_reset(css);
5150
5151        if (ss->css_offline)
5152                ss->css_offline(css);
5153
5154        css->flags &= ~CSS_ONLINE;
5155        RCU_INIT_POINTER(css->cgroup->subsys[ss->id], NULL);
5156
5157        wake_up_all(&css->cgroup->offline_waitq);
5158}
5159
5160/**
5161 * css_create - create a cgroup_subsys_state
5162 * @cgrp: the cgroup new css will be associated with
5163 * @ss: the subsys of new css
5164 *
5165 * Create a new css associated with @cgrp - @ss pair.  On success, the new
5166 * css is online and installed in @cgrp.  This function doesn't create the
5167 * interface files.  Returns 0 on success, -errno on failure.
5168 */
5169static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
5170                                              struct cgroup_subsys *ss)
5171{
5172        struct cgroup *parent = cgroup_parent(cgrp);
5173        struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
5174        struct cgroup_subsys_state *css;
5175        int err;
5176
5177        lockdep_assert_held(&cgroup_mutex);
5178
5179        css = ss->css_alloc(parent_css);
5180        if (!css)
5181                css = ERR_PTR(-ENOMEM);
5182        if (IS_ERR(css))
5183                return css;
5184
5185        init_and_link_css(css, ss, cgrp);
5186
5187        err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
5188        if (err)
5189                goto err_free_css;
5190
5191        err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
5192        if (err < 0)
5193                goto err_free_css;
5194        css->id = err;
5195
5196        /* @css is ready to be brought online now, make it visible */
5197        list_add_tail_rcu(&css->sibling, &parent_css->children);
5198        cgroup_idr_replace(&ss->css_idr, css, css->id);
5199
5200        err = online_css(css);
5201        if (err)
5202                goto err_list_del;
5203
5204        if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
5205            cgroup_parent(parent)) {
5206                pr_warn("%s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
5207                        current->comm, current->pid, ss->name);
5208                if (!strcmp(ss->name, "memory"))
5209                        pr_warn("\"memory\" requires setting use_hierarchy to 1 on the root\n");
5210                ss->warned_broken_hierarchy = true;
5211        }
5212
5213        return css;
5214
5215err_list_del:
5216        list_del_rcu(&css->sibling);
5217err_free_css:
5218        call_rcu(&css->rcu_head, css_free_rcu_fn);
5219        return ERR_PTR(err);
5220}
5221
5222static struct cgroup *cgroup_create(struct cgroup *parent)
5223{
5224        struct cgroup_root *root = parent->root;
5225        struct cgroup *cgrp, *tcgrp;
5226        int level = parent->level + 1;
5227        int ret;
5228
5229        /* allocate the cgroup and its ID, 0 is reserved for the root */
5230        cgrp = kzalloc(sizeof(*cgrp) +
5231                       sizeof(cgrp->ancestor_ids[0]) * (level + 1), GFP_KERNEL);
5232        if (!cgrp)
5233                return ERR_PTR(-ENOMEM);
5234
5235        ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
5236        if (ret)
5237                goto out_free_cgrp;
5238
5239        /*
5240         * Temporarily set the pointer to NULL, so idr_find() won't return
5241         * a half-baked cgroup.
5242         */
5243        cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
5244        if (cgrp->id < 0) {
5245                ret = -ENOMEM;
5246                goto out_cancel_ref;
5247        }
5248
5249        init_cgroup_housekeeping(cgrp);
5250
5251        cgrp->self.parent = &parent->self;
5252        cgrp->root = root;
5253        cgrp->level = level;
5254
5255        for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp))
5256                cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
5257
5258        if (notify_on_release(parent))
5259                set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
5260
5261        if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags))
5262                set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);
5263
5264        cgrp->self.serial_nr = css_serial_nr_next++;
5265
5266        /* allocation complete, commit to creation */
5267        list_add_tail_rcu(&cgrp->self.sibling, &cgroup_parent(cgrp)->self.children);
5268        atomic_inc(&root->nr_cgrps);
5269        cgroup_get(parent);
5270
5271        /*
5272         * @cgrp is now fully operational.  If something fails after this
5273         * point, it'll be released via the normal destruction path.
5274         */
5275        cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
5276
5277        /*
5278         * On the default hierarchy, a child doesn't automatically inherit
5279         * subtree_control from the parent.  Each is configured manually.
5280         */
5281        if (!cgroup_on_dfl(cgrp))
5282                cgrp->subtree_control = cgroup_control(cgrp);
5283
5284        cgroup_propagate_control(cgrp);
5285
5286        /* @cgrp doesn't have dir yet so the following will only create csses */
5287        ret = cgroup_apply_control_enable(cgrp);
5288        if (ret)
5289                goto out_destroy;
5290
5291        return cgrp;
5292
5293out_cancel_ref:
5294        percpu_ref_exit(&cgrp->self.refcnt);
5295out_free_cgrp:
5296        kfree(cgrp);
5297        return ERR_PTR(ret);
5298out_destroy:
5299        cgroup_destroy_locked(cgrp);
5300        return ERR_PTR(ret);
5301}
5302
5303static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
5304                        umode_t mode)
5305{
5306        struct cgroup *parent, *cgrp;
5307        struct kernfs_node *kn;
5308        int ret;
5309
5310        /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
5311        if (strchr(name, '\n'))
5312                return -EINVAL;
5313
5314        parent = cgroup_kn_lock_live(parent_kn, false);
5315        if (!parent)
5316                return -ENODEV;
5317
5318        cgrp = cgroup_create(parent);
5319        if (IS_ERR(cgrp)) {
5320                ret = PTR_ERR(cgrp);
5321                goto out_unlock;
5322        }
5323
5324        /* create the directory */
5325        kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
5326        if (IS_ERR(kn)) {
5327                ret = PTR_ERR(kn);
5328                goto out_destroy;
5329        }
5330        cgrp->kn = kn;
5331
5332        /*
5333         * This extra ref will be put in cgroup_free_fn() and guarantees
5334         * that @cgrp->kn is always accessible.
5335         */
5336        kernfs_get(kn);
5337
5338        ret = cgroup_kn_set_ugid(kn);
5339        if (ret)
5340                goto out_destroy;
5341
5342        ret = css_populate_dir(&cgrp->self);
5343        if (ret)
5344                goto out_destroy;
5345
5346        ret = cgroup_apply_control_enable(cgrp);
5347        if (ret)
5348                goto out_destroy;
5349
5350        trace_cgroup_mkdir(cgrp);
5351
5352        /* let's create and online css's */
5353        kernfs_activate(kn);
5354
5355        ret = 0;
5356        goto out_unlock;
5357
5358out_destroy:
5359        cgroup_destroy_locked(cgrp);
5360out_unlock:
5361        cgroup_kn_unlock(parent_kn);
5362        return ret;
5363}
5364
5365/*
5366 * This is called when the refcnt of a css is confirmed to be killed.
5367 * css_tryget_online() is now guaranteed to fail.  Tell the subsystem to
5368 * initate destruction and put the css ref from kill_css().
5369 */
5370static void css_killed_work_fn(struct work_struct *work)
5371{
5372        struct cgroup_subsys_state *css =
5373                container_of(work, struct cgroup_subsys_state, destroy_work);
5374
5375        mutex_lock(&cgroup_mutex);
5376
5377        do {
5378                offline_css(css);
5379                css_put(css);
5380                /* @css can't go away while we're holding cgroup_mutex */
5381                css = css->parent;
5382        } while (css && atomic_dec_and_test(&css->online_cnt));
5383
5384        mutex_unlock(&cgroup_mutex);
5385}
5386
5387/* css kill confirmation processing requires process context, bounce */
5388static void css_killed_ref_fn(struct percpu_ref *ref)
5389{
5390        struct cgroup_subsys_state *css =
5391                container_of(ref, struct cgroup_subsys_state, refcnt);
5392
5393        if (atomic_dec_and_test(&css->online_cnt)) {
5394                INIT_WORK(&css->destroy_work, css_killed_work_fn);
5395                queue_work(cgroup_destroy_wq, &css->destroy_work);
5396        }
5397}
5398
5399/**
5400 * kill_css - destroy a css
5401 * @css: css to destroy
5402 *
5403 * This function initiates destruction of @css by removing cgroup interface
5404 * files and putting its base reference.  ->css_offline() will be invoked
5405 * asynchronously once css_tryget_online() is guaranteed to fail and when
5406 * the reference count reaches zero, @css will be released.
5407 */
5408static void kill_css(struct cgroup_subsys_state *css)
5409{
5410        lockdep_assert_held(&cgroup_mutex);
5411
5412        /*
5413         * This must happen before css is disassociated with its cgroup.
5414         * See seq_css() for details.
5415         */
5416        css_clear_dir(css);
5417
5418        /*
5419         * Killing would put the base ref, but we need to keep it alive
5420         * until after ->css_offline().
5421         */
5422        css_get(css);
5423
5424        /*
5425         * cgroup core guarantees that, by the time ->css_offline() is
5426         * invoked, no new css reference will be given out via
5427         * css_tryget_online().  We can't simply call percpu_ref_kill() and
5428         * proceed to offlining css's because percpu_ref_kill() doesn't
5429         * guarantee that the ref is seen as killed on all CPUs on return.
5430         *
5431         * Use percpu_ref_kill_and_confirm() to get notifications as each
5432         * css is confirmed to be seen as killed on all CPUs.
5433         */
5434        percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
5435}
5436
5437/**
5438 * cgroup_destroy_locked - the first stage of cgroup destruction
5439 * @cgrp: cgroup to be destroyed
5440 *
5441 * css's make use of percpu refcnts whose killing latency shouldn't be
5442 * exposed to userland and are RCU protected.  Also, cgroup core needs to
5443 * guarantee that css_tryget_online() won't succeed by the time
5444 * ->css_offline() is invoked.  To satisfy all the requirements,
5445 * destruction is implemented in the following two steps.
5446 *
5447 * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
5448 *     userland visible parts and start killing the percpu refcnts of
5449 *     css's.  Set up so that the next stage will be kicked off once all
5450 *     the percpu refcnts are confirmed to be killed.
5451 *
5452 * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the
5453 *     rest of destruction.  Once all cgroup references are gone, the
5454 *     cgroup is RCU-freed.
5455 *
5456 * This function implements s1.  After this step, @cgrp is gone as far as
5457 * the userland is concerned and a new cgroup with the same name may be
5458 * created.  As cgroup doesn't care about the names internally, this
5459 * doesn't cause any problem.
5460 */
5461static int cgroup_destroy_locked(struct cgroup *cgrp)
5462        __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
5463{
5464        struct cgroup_subsys_state *css;
5465        struct cgrp_cset_link *link;
5466        int ssid;
5467
5468        lockdep_assert_held(&cgroup_mutex);
5469
5470        /*
5471         * Only migration can raise populated from zero and we're already
5472         * holding cgroup_mutex.
5473         */
5474        if (cgroup_is_populated(cgrp))
5475                return -EBUSY;
5476
5477        /*
5478         * Make sure there's no live children.  We can't test emptiness of
5479         * ->self.children as dead children linger on it while being
5480         * drained; otherwise, "rmdir parent/child parent" may fail.
5481         */
5482        if (css_has_online_children(&cgrp->self))
5483                return -EBUSY;
5484
5485        /*
5486         * Mark @cgrp and the associated csets dead.  The former prevents
5487         * further task migration and child creation by disabling
5488         * cgroup_lock_live_group().  The latter makes the csets ignored by
5489         * the migration path.
5490         */
5491        cgrp->self.flags &= ~CSS_ONLINE;
5492
5493        spin_lock_irq(&css_set_lock);
5494        list_for_each_entry(link, &cgrp->cset_links, cset_link)
5495                link->cset->dead = true;
5496        spin_unlock_irq(&css_set_lock);
5497
5498        /* initiate massacre of all css's */
5499        for_each_css(css, ssid, cgrp)
5500                kill_css(css);
5501
5502        /*
5503         * Remove @cgrp directory along with the base files.  @cgrp has an
5504         * extra ref on its kn.
5505         */
5506        kernfs_remove(cgrp->kn);
5507
5508        check_for_release(cgroup_parent(cgrp));
5509
5510        /* put the base reference */
5511        percpu_ref_kill(&cgrp->self.refcnt);
5512
5513        return 0;
5514};
5515
5516static int cgroup_rmdir(struct kernfs_node *kn)
5517{
5518        struct cgroup *cgrp;
5519        int ret = 0;
5520
5521        cgrp = cgroup_kn_lock_live(kn, false);
5522        if (!cgrp)
5523                return 0;
5524
5525        ret = cgroup_destroy_locked(cgrp);
5526
5527        if (!ret)
5528                trace_cgroup_rmdir(cgrp);
5529
5530        cgroup_kn_unlock(kn);
5531        return ret;
5532}
5533
5534static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
5535        .remount_fs             = cgroup_remount,
5536        .show_options           = cgroup_show_options,
5537        .mkdir                  = cgroup_mkdir,
5538        .rmdir                  = cgroup_rmdir,
5539        .rename                 = cgroup_rename,
5540        .show_path              = cgroup_show_path,
5541};
5542
5543static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
5544{
5545        struct cgroup_subsys_state *css;
5546
5547        pr_debug("Initializing cgroup subsys %s\n", ss->name);
5548
5549        mutex_lock(&cgroup_mutex);
5550
5551        idr_init(&ss->css_idr);
5552        INIT_LIST_HEAD(&ss->cfts);
5553
5554        /* Create the root cgroup state for this subsystem */
5555        ss->root = &cgrp_dfl_root;
5556        css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
5557        /* We don't handle early failures gracefully */
5558        BUG_ON(IS_ERR(css));
5559        init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
5560
5561        /*
5562         * Root csses are never destroyed and we can't initialize
5563         * percpu_ref during early init.  Disable refcnting.
5564         */
5565        css->flags |= CSS_NO_REF;
5566
5567        if (early) {
5568                /* allocation can't be done safely during early init */
5569                css->id = 1;
5570        } else {
5571                css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
5572                BUG_ON(css->id < 0);
5573        }
5574
5575        /* Update the init_css_set to contain a subsys
5576         * pointer to this state - since the subsystem is
5577         * newly registered, all tasks and hence the
5578         * init_css_set is in the subsystem's root cgroup. */
5579        init_css_set.subsys[ss->id] = css;
5580
5581        have_fork_callback |= (bool)ss->fork << ss->id;
5582        have_exit_callback |= (bool)ss->exit << ss->id;
5583        have_free_callback |= (bool)ss->free << ss->id;
5584        have_canfork_callback |= (bool)ss->can_fork << ss->id;
5585
5586        /* At system boot, before all subsystems have been
5587         * registered, no tasks have been forked, so we don't
5588         * need to invoke fork callbacks here. */
5589        BUG_ON(!list_empty(&init_task.tasks));
5590
5591        BUG_ON(online_css(css));
5592
5593        mutex_unlock(&cgroup_mutex);
5594}
5595
5596/**
5597 * cgroup_init_early - cgroup initialization at system boot
5598 *
5599 * Initialize cgroups at system boot, and initialize any
5600 * subsystems that request early init.
5601 */
5602int __init cgroup_init_early(void)
5603{
5604        static struct cgroup_sb_opts __initdata opts;
5605        struct cgroup_subsys *ss;
5606        int i;
5607
5608        init_cgroup_root(&cgrp_dfl_root, &opts);
5609        cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
5610
5611        RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
5612
5613        for_each_subsys(ss, i) {
5614                WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
5615                     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
5616                     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
5617                     ss->id, ss->name);
5618                WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
5619                     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);
5620
5621                ss->id = i;
5622                ss->name = cgroup_subsys_name[i];
5623                if (!ss->legacy_name)
5624                        ss->legacy_name = cgroup_subsys_name[i];
5625
5626                if (ss->early_init)
5627                        cgroup_init_subsys(ss, true);
5628        }
5629        return 0;
5630}
5631
5632static u16 cgroup_disable_mask __initdata;
5633
5634/**
5635 * cgroup_init - cgroup initialization
5636 *
5637 * Register cgroup filesystem and /proc file, and initialize
5638 * any subsystems that didn't request early init.
5639 */
5640int __init cgroup_init(void)
5641{
5642        struct cgroup_subsys *ss;
5643        int ssid;
5644
5645        BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
5646        BUG_ON(percpu_init_rwsem(&cgroup_threadgroup_rwsem));
5647        BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
5648        BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
5649
5650        /*
5651         * The latency of the synchronize_sched() is too high for cgroups,
5652         * avoid it at the cost of forcing all readers into the slow path.
5653         */
5654        rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
5655
5656        get_user_ns(init_cgroup_ns.user_ns);
5657
5658        mutex_lock(&cgroup_mutex);
5659
5660        /*
5661         * Add init_css_set to the hash table so that dfl_root can link to
5662         * it during init.
5663         */
5664        hash_add(css_set_table, &init_css_set.hlist,
5665                 css_set_hash(init_css_set.subsys));
5666
5667        BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
5668
5669        mutex_unlock(&cgroup_mutex);
5670
5671        for_each_subsys(ss, ssid) {
5672                if (ss->early_init) {
5673                        struct cgroup_subsys_state *css =
5674                                init_css_set.subsys[ss->id];
5675
5676                        css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
5677                                                   GFP_KERNEL);
5678                        BUG_ON(css->id < 0);
5679                } else {
5680                        cgroup_init_subsys(ss, false);
5681                }
5682
5683                list_add_tail(&init_css_set.e_cset_node[ssid],
5684                              &cgrp_dfl_root.cgrp.e_csets[ssid]);
5685
5686                /*
5687                 * Setting dfl_root subsys_mask needs to consider the
5688                 * disabled flag and cftype registration needs kmalloc,
5689                 * both of which aren't available during early_init.
5690                 */
5691                if (cgroup_disable_mask & (1 << ssid)) {
5692                        static_branch_disable(cgroup_subsys_enabled_key[ssid]);
5693                        printk(KERN_INFO "Disabling %s control group subsystem\n",
5694                               ss->name);
5695                        continue;
5696                }
5697
5698                if (cgroup_ssid_no_v1(ssid))
5699                        printk(KERN_INFO "Disabling %s control group subsystem in v1 mounts\n",
5700                               ss->name);
5701
5702                cgrp_dfl_root.subsys_mask |= 1 << ss->id;
5703
5704                if (ss->implicit_on_dfl)
5705                        cgrp_dfl_implicit_ss_mask |= 1 << ss->id;
5706                else if (!ss->dfl_cftypes)
5707                        cgrp_dfl_inhibit_ss_mask |= 1 << ss->id;
5708
5709                if (ss->dfl_cftypes == ss->legacy_cftypes) {
5710                        WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
5711                } else {
5712                        WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
5713                        WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
5714                }
5715
5716                if (ss->bind)
5717                        ss->bind(init_css_set.subsys[ssid]);
5718        }
5719
5720        /* init_css_set.subsys[] has been updated, re-hash */
5721        hash_del(&init_css_set.hlist);
5722        hash_add(css_set_table, &init_css_set.hlist,
5723                 css_set_hash(init_css_set.subsys));
5724
5725        WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
5726        WARN_ON(register_filesystem(&cgroup_fs_type));
5727        WARN_ON(register_filesystem(&cgroup2_fs_type));
5728        WARN_ON(!proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations));
5729
5730        return 0;
5731}
5732
5733static int __init cgroup_wq_init(void)
5734{
5735        /*
5736         * There isn't much point in executing destruction path in
5737         * parallel.  Good chunk is serialized with cgroup_mutex anyway.
5738         * Use 1 for @max_active.
5739         *
5740         * We would prefer to do this in cgroup_init() above, but that
5741         * is called before init_workqueues(): so leave this until after.
5742         */
5743        cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
5744        BUG_ON(!cgroup_destroy_wq);
5745
5746        /*
5747         * Used to destroy pidlists and separate to serve as flush domain.
5748         * Cap @max_active to 1 too.
5749         */
5750        cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy",
5751                                                    0, 1);
5752        BUG_ON(!cgroup_pidlist_destroy_wq);
5753
5754        return 0;
5755}
5756core_initcall(cgroup_wq_init);
5757
5758/*
5759 * proc_cgroup_show()
5760 *  - Print task's cgroup paths into seq_file, one line for each hierarchy
5761 *  - Used for /proc/<pid>/cgroup.
5762 */
5763int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
5764                     struct pid *pid, struct task_struct *tsk)
5765{
5766        char *buf;
5767        int retval;
5768        struct cgroup_root *root;
5769
5770        retval = -ENOMEM;
5771        buf = kmalloc(PATH_MAX, GFP_KERNEL);
5772        if (!buf)
5773                goto out;
5774
5775        mutex_lock(&cgroup_mutex);
5776        spin_lock_irq(&css_set_lock);
5777
5778        for_each_root(root) {
5779                struct cgroup_subsys *ss;
5780                struct cgroup *cgrp;
5781                int ssid, count = 0;
5782
5783                if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
5784                        continue;
5785
5786                seq_printf(m, "%d:", root->hierarchy_id);
5787                if (root != &cgrp_dfl_root)
5788                        for_each_subsys(ss, ssid)
5789                                if (root->subsys_mask & (1 << ssid))
5790                                        seq_printf(m, "%s%s", count++ ? "," : "",
5791                                                   ss->legacy_name);
5792                if (strlen(root->name))
5793                        seq_printf(m, "%sname=%s", count ? "," : "",
5794                                   root->name);
5795                seq_putc(m, ':');
5796
5797                cgrp = task_cgroup_from_root(tsk, root);
5798
5799                /*
5800                 * On traditional hierarchies, all zombie tasks show up as
5801                 * belonging to the root cgroup.  On the default hierarchy,
5802                 * while a zombie doesn't show up in "cgroup.procs" and
5803                 * thus can't be migrated, its /proc/PID/cgroup keeps
5804                 * reporting the cgroup it belonged to before exiting.  If
5805                 * the cgroup is removed before the zombie is reaped,
5806                 * " (deleted)" is appended to the cgroup path.
5807                 */
5808                if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) {
5809                        retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX,
5810                                                current->nsproxy->cgroup_ns);
5811                        if (retval >= PATH_MAX)
5812                                retval = -ENAMETOOLONG;
5813                        if (retval < 0)
5814                                goto out_unlock;
5815
5816                        seq_puts(m, buf);
5817                } else {
5818                        seq_puts(m, "/");
5819                }
5820
5821                if (cgroup_on_dfl(cgrp) && cgroup_is_dead(cgrp))
5822                        seq_puts(m, " (deleted)\n");
5823                else
5824                        seq_putc(m, '\n');
5825        }
5826
5827        retval = 0;
5828out_unlock:
5829        spin_unlock_irq(&css_set_lock);
5830        mutex_unlock(&cgroup_mutex);
5831        kfree(buf);
5832out:
5833        return retval;
5834}
5835
5836/* Display information about each subsystem and each hierarchy */
5837static int proc_cgroupstats_show(struct seq_file *m, void *v)
5838{
5839        struct cgroup_subsys *ss;
5840        int i;
5841
5842        seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
5843        /*
5844         * ideally we don't want subsystems moving around while we do this.
5845         * cgroup_mutex is also necessary to guarantee an atomic snapshot of
5846         * subsys/hierarchy state.
5847         */
5848        mutex_lock(&cgroup_mutex);
5849
5850        for_each_subsys(ss, i)
5851                seq_printf(m, "%s\t%d\t%d\t%d\n",
5852                           ss->legacy_name, ss->root->hierarchy_id,
5853                           atomic_read(&ss->root->nr_cgrps),
5854                           cgroup_ssid_enabled(i));
5855
5856        mutex_unlock(&cgroup_mutex);
5857        return 0;
5858}
5859
5860static int cgroupstats_open(struct inode *inode, struct file *file)
5861{
5862        return single_open(file, proc_cgroupstats_show, NULL);
5863}
5864
5865static const struct file_operations proc_cgroupstats_operations = {
5866        .open = cgroupstats_open,
5867        .read = seq_read,
5868        .llseek = seq_lseek,
5869        .release = single_release,
5870};
5871
5872/**
5873 * cgroup_fork - initialize cgroup related fields during copy_process()
5874 * @child: pointer to task_struct of forking parent process.
5875 *
5876 * A task is associated with the init_css_set until cgroup_post_fork()
5877 * attaches it to the parent's css_set.  Empty cg_list indicates that
5878 * @child isn't holding reference to its css_set.
5879 */
5880void cgroup_fork(struct task_struct *child)
5881{
5882        RCU_INIT_POINTER(child->cgroups, &init_css_set);
5883        INIT_LIST_HEAD(&child->cg_list);
5884}
5885
5886/**
5887 * cgroup_can_fork - called on a new task before the process is exposed
5888 * @child: the task in question.
5889 *
5890 * This calls the subsystem can_fork() callbacks. If the can_fork() callback
5891 * returns an error, the fork aborts with that error code. This allows for
5892 * a cgroup subsystem to conditionally allow or deny new forks.
5893 */
5894int cgroup_can_fork(struct task_struct *child)
5895{
5896        struct cgroup_subsys *ss;
5897        int i, j, ret;
5898
5899        do_each_subsys_mask(ss, i, have_canfork_callback) {
5900                ret = ss->can_fork(child);
5901                if (ret)
5902                        goto out_revert;
5903        } while_each_subsys_mask();
5904
5905        return 0;
5906
5907out_revert:
5908        for_each_subsys(ss, j) {
5909                if (j >= i)
5910                        break;
5911                if (ss->cancel_fork)
5912                        ss->cancel_fork(child);
5913        }
5914
5915        return ret;
5916}
5917
5918/**
5919 * cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
5920 * @child: the task in question
5921 *
5922 * This calls the cancel_fork() callbacks if a fork failed *after*
5923 * cgroup_can_fork() succeded.
5924 */
5925void cgroup_cancel_fork(struct task_struct *child)
5926{
5927        struct cgroup_subsys *ss;
5928        int i;
5929
5930        for_each_subsys(ss, i)
5931                if (ss->cancel_fork)
5932                        ss->cancel_fork(child);
5933}
5934
5935/**
5936 * cgroup_post_fork - called on a new task after adding it to the task list
5937 * @child: the task in question
5938 *
5939 * Adds the task to the list running through its css_set if necessary and
5940 * call the subsystem fork() callbacks.  Has to be after the task is
5941 * visible on the task list in case we race with the first call to
5942 * cgroup_task_iter_start() - to guarantee that the new task ends up on its
5943 * list.
5944 */
5945void cgroup_post_fork(struct task_struct *child)
5946{
5947        struct cgroup_subsys *ss;
5948        int i;
5949
5950        /*
5951         * This may race against cgroup_enable_task_cg_lists().  As that
5952         * function sets use_task_css_set_links before grabbing
5953         * tasklist_lock and we just went through tasklist_lock to add
5954         * @child, it's guaranteed that either we see the set
5955         * use_task_css_set_links or cgroup_enable_task_cg_lists() sees
5956         * @child during its iteration.
5957         *
5958         * If we won the race, @child is associated with %current's
5959         * css_set.  Grabbing css_set_lock guarantees both that the
5960         * association is stable, and, on completion of the parent's
5961         * migration, @child is visible in the source of migration or
5962         * already in the destination cgroup.  This guarantee is necessary
5963         * when implementing operations which need to migrate all tasks of
5964         * a cgroup to another.
5965         *
5966         * Note that if we lose to cgroup_enable_task_cg_lists(), @child
5967         * will remain in init_css_set.  This is safe because all tasks are
5968         * in the init_css_set before cg_links is enabled and there's no
5969         * operation which transfers all tasks out of init_css_set.
5970         */
5971        if (use_task_css_set_links) {
5972                struct css_set *cset;
5973
5974                spin_lock_irq(&css_set_lock);
5975                cset = task_css_set(current);
5976                if (list_empty(&child->cg_list)) {
5977                        get_css_set(cset);
5978                        css_set_move_task(child, NULL, cset, false);
5979                }
5980                spin_unlock_irq(&css_set_lock);
5981        }
5982
5983        /*
5984         * Call ss->fork().  This must happen after @child is linked on
5985         * css_set; otherwise, @child might change state between ->fork()
5986         * and addition to css_set.
5987         */
5988        do_each_subsys_mask(ss, i, have_fork_callback) {
5989                ss->fork(child);
5990        } while_each_subsys_mask();
5991}
5992
5993/**
5994 * cgroup_exit - detach cgroup from exiting task
5995 * @tsk: pointer to task_struct of exiting process
5996 *
5997 * Description: Detach cgroup from @tsk and release it.
5998 *
5999 * Note that cgroups marked notify_on_release force every task in
6000 * them to take the global cgroup_mutex mutex when exiting.
6001 * This could impact scaling on very large systems.  Be reluctant to
6002 * use notify_on_release cgroups where very high task exit scaling
6003 * is required on large systems.
6004 *
6005 * We set the exiting tasks cgroup to the root cgroup (top_cgroup).  We
6006 * call cgroup_exit() while the task is still competent to handle
6007 * notify_on_release(), then leave the task attached to the root cgroup in
6008 * each hierarchy for the remainder of its exit.  No need to bother with
6009 * init_css_set refcnting.  init_css_set never goes away and we can't race
6010 * with migration path - PF_EXITING is visible to migration path.
6011 */
6012void cgroup_exit(struct task_struct *tsk)
6013{
6014        struct cgroup_subsys *ss;
6015        struct css_set *cset;
6016        int i;
6017
6018        /*
6019         * Unlink from @tsk from its css_set.  As migration path can't race
6020         * with us, we can check css_set and cg_list without synchronization.
6021         */
6022        cset = task_css_set(tsk);
6023
6024        if (!list_empty(&tsk->cg_list)) {
6025