lib/lockref.c

   1 #include <linux/export.h>
   2 #include <linux/lockref.h>
   3
   4 #ifdef CONFIG_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 = ACCESS_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 = cmpxchg(&lockref->lock_count,                  \
  18                                          old.lock_count, new.lock_count);       \
  19                 if (likely(old.lock_count == prev.lock_count)) {                \
  20                         SUCCESS;                                                \
  21                 }                                                               \
  22         }                                                                       \
  23 } while (0)
  24
  25 #else
  26
  27 #define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
  28
  29 #endif
  30
  31 /**
  32  * lockref_get - Increments reference count unconditionally
  33  * @lockcnt: pointer to lockref structure
  34  *
  35  * This operation is only valid if you already hold a reference
  36  * to the object, so you know the count cannot be zero.
  37  */
  38 void lockref_get(struct lockref *lockref)
  39 {
  40         CMPXCHG_LOOP(
  41                 new.count++;
  42         ,
  43                 return;
  44         );
  45
  46         spin_lock(&lockref->lock);
  47         lockref->count++;
  48         spin_unlock(&lockref->lock);
  49 }
  50 EXPORT_SYMBOL(lockref_get);
  51
  52 /**
  53  * lockref_get_not_zero - Increments count unless the count is 0
  54  * @lockcnt: pointer to lockref structure
  55  * Return: 1 if count updated successfully or 0 if count was zero
  56  */
  57 int lockref_get_not_zero(struct lockref *lockref)
  58 {
  59         int retval;
  60
  61         CMPXCHG_LOOP(
  62                 new.count++;
  63                 if (!old.count)
  64                         return 0;
  65         ,
  66                 return 1;
  67         );
  68
  69         spin_lock(&lockref->lock);
  70         retval = 0;
  71         if (lockref->count) {
  72                 lockref->count++;
  73                 retval = 1;
  74         }
  75         spin_unlock(&lockref->lock);
  76         return retval;
  77 }
  78 EXPORT_SYMBOL(lockref_get_not_zero);
  79
  80 /**
  81  * lockref_get_or_lock - Increments count unless the count is 0
  82  * @lockcnt: pointer to lockref structure
  83  * Return: 1 if count updated successfully or 0 if count was zero
  84  * and we got the lock instead.
  85  */
  86 int lockref_get_or_lock(struct lockref *lockref)
  87 {
  88         CMPXCHG_LOOP(
  89                 new.count++;
  90                 if (!old.count)
  91                         break;
  92         ,
  93                 return 1;
  94         );
  95
  96         spin_lock(&lockref->lock);
  97         if (!lockref->count)
  98                 return 0;
  99         lockref->count++;
 100         spin_unlock(&lockref->lock);
 101         return 1;
 102 }
 103 EXPORT_SYMBOL(lockref_get_or_lock);
 104
 105 /**
 106  * lockref_put_or_lock - decrements count unless count <= 1 before decrement
 107  * @lockcnt: pointer to lockref structure
 108  * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
 109  */
 110 int lockref_put_or_lock(struct lockref *lockref)
 111 {
 112         CMPXCHG_LOOP(
 113                 new.count--;
 114                 if (old.count <= 1)
 115                         break;
 116         ,
 117                 return 1;
 118         );
 119
 120         spin_lock(&lockref->lock);
 121         if (lockref->count <= 1)
 122                 return 0;
 123         lockref->count--;
 124         spin_unlock(&lockref->lock);
 125         return 1;
 126 }
 127 EXPORT_SYMBOL(lockref_put_or_lock);