[deliverable/linux.git] / include / linux / lockref.h

#ifndef __LINUX_LOCKREF_H
#define __LINUX_LOCKREF_H

/*
 * Locked reference counts.
 *
 * These are different from just plain atomic refcounts in that they
 * are atomic with respect to the spinlock that goes with them.  In
 * particular, there can be implementations that don't actually get
 * the spinlock for the common decrement/increment operations, but they
 * still have to check that the operation is done semantically as if
 * the spinlock had been taken (using a cmpxchg operation that covers
 * both the lock and the count word, or using memory transactions, for
 * example).
 */

#include <linux/spinlock.h>
#include <generated/bounds.h>

#define USE_CMPXCHG_LOCKREF \
	(IS_ENABLED(CONFIG_ARCH_USE_CMPXCHG_LOCKREF) && \
	 IS_ENABLED(CONFIG_SMP) && SPINLOCK_SIZE <= 4)

struct lockref {
	union {
#if USE_CMPXCHG_LOCKREF
		aligned_u64 lock_count;
#endif
		struct {
			spinlock_t lock;
			unsigned int count;
		};
	};
};

extern void lockref_get(struct lockref *);
extern int lockref_get_not_zero(struct lockref *);
extern int lockref_get_or_lock(struct lockref *);
extern int lockref_put_or_lock(struct lockref *);

extern void lockref_mark_dead(struct lockref *);
extern int lockref_get_not_dead(struct lockref *);

/* Must be called under spinlock for reliable results */
static inline int __lockref_is_dead(const struct lockref *l)
{
	return ((int)l->count < 0);
}

#endif /* __LINUX_LOCKREF_H */
Commit	Line	Data
	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 */