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