include/linux/lockref.h

   1 #ifndef __LINUX_LOCKREF_H
   2 #define __LINUX_LOCKREF_H
   3
   4 /*
   5  * Locked reference counts.
   6  *
   7  * These are different from just plain atomic refcounts in that they
   8  * are atomic with respect to the spinlock that goes with them.  In
   9  * particular, there can be implementations that don't actually get
  10  * the spinlock for the common decrement/increment operations, but they
  11  * still have to check that the operation is done semantically as if
  12  * the spinlock had been taken (using a cmpxchg operation that covers
  13  * both the lock and the count word, or using memory transactions, for
  14  * example).
  15  */
  16
  17 #include <linux/spinlock.h>
  18 #include <generated/bounds.h>
  19
  20 #define USE_CMPXCHG_LOCKREF \
  21         (IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \
  22          IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4)
  23
  24 struct lockref {
  25         union {
  26 #if USE_CMPXCHG_LOCKREF
  27                 aligned_u64 lock_count;
  28 #endif
  29                 struct {
  30                         spinlock_t lock;
  31                         unsigned int count;
  32                 };
  33         };
  34 };
  35
  36 extern void lockref_get(struct lockref *);
  37 extern int lockref_get_not_zero(struct lockref *);
  38 extern int lockref_get_or_lock(struct lockref *);
  39 extern int lockref_put_or_lock(struct lockref *);
  40
  41 extern void lockref_mark_dead(struct lockref *);
  42 extern int lockref_get_not_dead(struct lockref *);
  43
  44 /* Must be called under spinlock for reliable results */
  45 static inline int __lockref_is_dead(const struct lockref *l)
  46 {
  47         return ((int)l->count < 0);
  48 }
  49
  50 #endif /* __LINUX_LOCKREF_H */