LXR linux/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
  24struct lockref {
  25        union {
  26#if USE_CMPXCHG_LOCKREF
  27                aligned_u64 lock_count;
  28#endif
  29                struct {
  30                        spinlock_t lock;
  31                        int count;
  32                };
  33        };
  34};
  35
  36extern void lockref_get(struct lockref *);
  37extern int lockref_put_return(struct lockref *);
  38extern int lockref_get_not_zero(struct lockref *);
  39extern int lockref_get_or_lock(struct lockref *);
  40extern int lockref_put_or_lock(struct lockref *);
  41
  42extern void lockref_mark_dead(struct lockref *);
  43extern int lockref_get_not_dead(struct lockref *);
  44
  45/* Must be called under spinlock for reliable results */
  46static inline int __lockref_is_dead(const struct lockref *l)
  47{
  48        return ((int)l->count < 0);
  49}
  50
  51#endif /* __LINUX_LOCKREF_H */
  52