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TOMOYO Linux Cross Reference
Linux/include/linux/lockref.h

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  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                         int count;
 32                 };
 33         };
 34 };
 35 
 36 extern void lockref_get(struct lockref *);
 37 extern int lockref_put_return(struct lockref *);
 38 extern int lockref_get_not_zero(struct lockref *);
 39 extern int lockref_get_or_lock(struct lockref *);
 40 extern int lockref_put_or_lock(struct lockref *);
 41 
 42 extern void lockref_mark_dead(struct lockref *);
 43 extern int lockref_get_not_dead(struct lockref *);
 44 
 45 /* Must be called under spinlock for reliable results */
 46 static inline int __lockref_is_dead(const struct lockref *l)
 47 {
 48         return ((int)l->count < 0);
 49 }
 50 
 51 #endif /* __LINUX_LOCKREF_H */
 52 

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