include/linux/lockref.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __LINUX_LOCKREF_H
   3 #define __LINUX_LOCKREF_H
   4
   5 /*
   6  * Locked reference counts.
   7  *
   8  * These are different from just plain atomic refcounts in that they
   9  * are atomic with respect to the spinlock that goes with them.  In
  10  * particular, there can be implementations that don't actually get
  11  * the spinlock for the common decrement/increment operations, but they
  12  * still have to check that the operation is done semantically as if
  13  * the spinlock had been taken (using a cmpxchg operation that covers
  14  * both the lock and the count word, or using memory transactions, for
  15  * example).
  16  */
  17
  18 #include <linux/spinlock.h>
  19 #include <generated/bounds.h>
  20
  21 #define USE_CMPXCHG_LOCKREF \
  22         (IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \
  23          IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4)
  24
  25 struct lockref {
  26         union {
  27 #if USE_CMPXCHG_LOCKREF
  28                 aligned_u64 lock_count;
  29 #endif
  30                 struct {
  31                         spinlock_t lock;
  32                         int count;
  33                 };
  34         };
  35 };
  36
  37 extern void lockref_get(struct lockref *);
  38 extern int lockref_put_return(struct lockref *);
  39 extern int lockref_get_not_zero(struct lockref *);
  40 extern int lockref_get_or_lock(struct lockref *);
  41 extern int lockref_put_or_lock(struct lockref *);
  42
  43 extern void lockref_mark_dead(struct lockref *);
  44 extern int lockref_get_not_dead(struct lockref *);
  45
  46 /* Must be called under spinlock for reliable results */
  47 static inline int __lockref_is_dead(const struct lockref *l)
  48 {
  49         return ((int)l->count < 0);
  50 }
  51
  52 #endif /* __LINUX_LOCKREF_H */