linux/lib/lockref.c
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   1#include <linux/export.h>
   2#include <linux/lockref.h>
   3
   4#if USE_CMPXCHG_LOCKREF
   5
   6/*
   7 * Note that the "cmpxchg()" reloads the "old" value for the
   8 * failure case.
   9 */
  10#define CMPXCHG_LOOP(CODE, SUCCESS) do {                                        \
  11        struct lockref old;                                                     \
  12        BUILD_BUG_ON(sizeof(old) != 8);                                         \
  13        old.lock_count = READ_ONCE(lockref->lock_count);                        \
  14        while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) {     \
  15                struct lockref new = old, prev = old;                           \
  16                CODE                                                            \
  17                old.lock_count = cmpxchg64_relaxed(&lockref->lock_count,        \
  18                                                   old.lock_count,              \
  19                                                   new.lock_count);             \
  20                if (likely(old.lock_count == prev.lock_count)) {                \
  21                        SUCCESS;                                                \
  22                }                                                               \
  23                cpu_relax_lowlatency();                                         \
  24        }                                                                       \
  25} while (0)
  26
  27#else
  28
  29#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
  30
  31#endif
  32
  33/**
  34 * lockref_get - Increments reference count unconditionally
  35 * @lockref: pointer to lockref structure
  36 *
  37 * This operation is only valid if you already hold a reference
  38 * to the object, so you know the count cannot be zero.
  39 */
  40void lockref_get(struct lockref *lockref)
  41{
  42        CMPXCHG_LOOP(
  43                new.count++;
  44        ,
  45                return;
  46        );
  47
  48        spin_lock(&lockref->lock);
  49        lockref->count++;
  50        spin_unlock(&lockref->lock);
  51}
  52EXPORT_SYMBOL(lockref_get);
  53
  54/**
  55 * lockref_get_not_zero - Increments count unless the count is 0 or dead
  56 * @lockref: pointer to lockref structure
  57 * Return: 1 if count updated successfully or 0 if count was zero
  58 */
  59int lockref_get_not_zero(struct lockref *lockref)
  60{
  61        int retval;
  62
  63        CMPXCHG_LOOP(
  64                new.count++;
  65                if (old.count <= 0)
  66                        return 0;
  67        ,
  68                return 1;
  69        );
  70
  71        spin_lock(&lockref->lock);
  72        retval = 0;
  73        if (lockref->count > 0) {
  74                lockref->count++;
  75                retval = 1;
  76        }
  77        spin_unlock(&lockref->lock);
  78        return retval;
  79}
  80EXPORT_SYMBOL(lockref_get_not_zero);
  81
  82/**
  83 * lockref_get_or_lock - Increments count unless the count is 0 or dead
  84 * @lockref: pointer to lockref structure
  85 * Return: 1 if count updated successfully or 0 if count was zero
  86 * and we got the lock instead.
  87 */
  88int lockref_get_or_lock(struct lockref *lockref)
  89{
  90        CMPXCHG_LOOP(
  91                new.count++;
  92                if (old.count <= 0)
  93                        break;
  94        ,
  95                return 1;
  96        );
  97
  98        spin_lock(&lockref->lock);
  99        if (lockref->count <= 0)
 100                return 0;
 101        lockref->count++;
 102        spin_unlock(&lockref->lock);
 103        return 1;
 104}
 105EXPORT_SYMBOL(lockref_get_or_lock);
 106
 107/**
 108 * lockref_put_return - Decrement reference count if possible
 109 * @lockref: pointer to lockref structure
 110 *
 111 * Decrement the reference count and return the new value.
 112 * If the lockref was dead or locked, return an error.
 113 */
 114int lockref_put_return(struct lockref *lockref)
 115{
 116        CMPXCHG_LOOP(
 117                new.count--;
 118                if (old.count <= 0)
 119                        return -1;
 120        ,
 121                return new.count;
 122        );
 123        return -1;
 124}
 125EXPORT_SYMBOL(lockref_put_return);
 126
 127/**
 128 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
 129 * @lockref: pointer to lockref structure
 130 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
 131 */
 132int lockref_put_or_lock(struct lockref *lockref)
 133{
 134        CMPXCHG_LOOP(
 135                new.count--;
 136                if (old.count <= 1)
 137                        break;
 138        ,
 139                return 1;
 140        );
 141
 142        spin_lock(&lockref->lock);
 143        if (lockref->count <= 1)
 144                return 0;
 145        lockref->count--;
 146        spin_unlock(&lockref->lock);
 147        return 1;
 148}
 149EXPORT_SYMBOL(lockref_put_or_lock);
 150
 151/**
 152 * lockref_mark_dead - mark lockref dead
 153 * @lockref: pointer to lockref structure
 154 */
 155void lockref_mark_dead(struct lockref *lockref)
 156{
 157        assert_spin_locked(&lockref->lock);
 158        lockref->count = -128;
 159}
 160EXPORT_SYMBOL(lockref_mark_dead);
 161
 162/**
 163 * lockref_get_not_dead - Increments count unless the ref is dead
 164 * @lockref: pointer to lockref structure
 165 * Return: 1 if count updated successfully or 0 if lockref was dead
 166 */
 167int lockref_get_not_dead(struct lockref *lockref)
 168{
 169        int retval;
 170
 171        CMPXCHG_LOOP(
 172                new.count++;
 173                if (old.count < 0)
 174                        return 0;
 175        ,
 176                return 1;
 177        );
 178
 179        spin_lock(&lockref->lock);
 180        retval = 0;
 181        if (lockref->count >= 0) {
 182                lockref->count++;
 183                retval = 1;
 184        }
 185        spin_unlock(&lockref->lock);
 186        return retval;
 187}
 188EXPORT_SYMBOL(lockref_get_not_dead);
 189