lib/lockref.c

   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  */
  40 void 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 }
  52 EXPORT_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  */
  59 int 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 }
  80 EXPORT_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  */
  88 int 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 }
 105 EXPORT_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  */
 114 int 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 }
 125 EXPORT_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  */
 132 int 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 }
 149 EXPORT_SYMBOL(lockref_put_or_lock);
 150
 151 /**
 152  * lockref_mark_dead - mark lockref dead
 153  * @lockref: pointer to lockref structure
 154  */
 155 void lockref_mark_dead(struct lockref *lockref)
 156 {
 157         assert_spin_locked(&lockref->lock);
 158         lockref->count = -128;
 159 }
 160 EXPORT_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  */
 167 int 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 }
 188 EXPORT_SYMBOL(lockref_get_not_dead);