[linux.git] / lib / lockref.c

#include <linux/export.h>
#include <linux/lockref.h>

#ifdef CONFIG_CMPXCHG_LOCKREF

/*
 * Note that the "cmpxchg()" reloads the "old" value for the
 * failure case.
 */
#define CMPXCHG_LOOP(CODE, SUCCESS) do {					\
	struct lockref old;							\
	BUILD_BUG_ON(sizeof(old) != 8);						\
	old.lock_count = ACCESS_ONCE(lockref->lock_count);			\
	while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) {  	\
		struct lockref new = old, prev = old;				\
		CODE								\
		old.lock_count = cmpxchg(&lockref->lock_count,			\
					 old.lock_count, new.lock_count);	\
		if (likely(old.lock_count == prev.lock_count)) {		\
			SUCCESS;						\
		}								\
		cpu_relax();							\
	}									\
} while (0)

#else

#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)

#endif

/**
 * lockref_get - Increments reference count unconditionally
 * @lockcnt: pointer to lockref structure
 *
 * This operation is only valid if you already hold a reference
 * to the object, so you know the count cannot be zero.
 */
void lockref_get(struct lockref *lockref)
{
	CMPXCHG_LOOP(
		new.count++;
	,
		return;
	);

	spin_lock(&lockref->lock);
	lockref->count++;
	spin_unlock(&lockref->lock);
}
EXPORT_SYMBOL(lockref_get);

/**
 * lockref_get_not_zero - Increments count unless the count is 0
 * @lockcnt: pointer to lockref structure
 * Return: 1 if count updated successfully or 0 if count was zero
 */
int lockref_get_not_zero(struct lockref *lockref)
{
	int retval;

	CMPXCHG_LOOP(
		new.count++;
		if (!old.count)
			return 0;
	,
		return 1;
	);

	spin_lock(&lockref->lock);
	retval = 0;
	if (lockref->count) {
		lockref->count++;
		retval = 1;
	}
	spin_unlock(&lockref->lock);
	return retval;
}
EXPORT_SYMBOL(lockref_get_not_zero);

/**
 * lockref_get_or_lock - Increments count unless the count is 0
 * @lockcnt: pointer to lockref structure
 * Return: 1 if count updated successfully or 0 if count was zero
 * and we got the lock instead.
 */
int lockref_get_or_lock(struct lockref *lockref)
{
	CMPXCHG_LOOP(
		new.count++;
		if (!old.count)
			break;
	,
		return 1;
	);

	spin_lock(&lockref->lock);
	if (!lockref->count)
		return 0;
	lockref->count++;
	spin_unlock(&lockref->lock);
	return 1;
}
EXPORT_SYMBOL(lockref_get_or_lock);

/**
 * lockref_put_or_lock - decrements count unless count <= 1 before decrement
 * @lockcnt: pointer to lockref structure
 * Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
 */
int lockref_put_or_lock(struct lockref *lockref)
{
	CMPXCHG_LOOP(
		new.count--;
		if (old.count <= 1)
			break;
	,
		return 1;
	);

	spin_lock(&lockref->lock);
	if (lockref->count <= 1)
		return 0;
	lockref->count--;
	spin_unlock(&lockref->lock);
	return 1;
}
EXPORT_SYMBOL(lockref_put_or_lock);
Commit	Line	Data
2f4f12e5 LT	1	#include <linux/export.h>
	2	#include <linux/lockref.h>
	3
bc08b449 LT	4	#ifdef CONFIG_CMPXCHG_LOCKREF
	5
	6	/*
	7	* Note that the "cmpxchg()" reloads the "old" value for the
	8	* failure case.
	9	*/
	10	#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
	11	struct lockref old; \
	12	BUILD_BUG_ON(sizeof(old) != 8); \
	13	old.lock_count = ACCESS_ONCE(lockref->lock_count); \
	14	while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
	15	struct lockref new = old, prev = old; \
	16	CODE \
	17	old.lock_count = cmpxchg(&lockref->lock_count, \
	18	old.lock_count, new.lock_count); \
	19	if (likely(old.lock_count == prev.lock_count)) { \
	20	SUCCESS; \
	21	} \
d472d9d9	22	cpu_relax(); \
bc08b449 LT	23	} \
	24	} while (0)
	25
	26	#else
	27
	28	#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
	29
	30	#endif
	31
2f4f12e5 LT	32	/**
	33	* lockref_get - Increments reference count unconditionally
	34	* @lockcnt: pointer to lockref structure
	35	*
	36	* This operation is only valid if you already hold a reference
	37	* to the object, so you know the count cannot be zero.
	38	*/
	39	void lockref_get(struct lockref *lockref)
	40	{
bc08b449 LT	41	CMPXCHG_LOOP(
	42	new.count++;
	43	,
	44	return;
	45	);
	46
2f4f12e5 LT	47	spin_lock(&lockref->lock);
	48	lockref->count++;
	49	spin_unlock(&lockref->lock);
	50	}
	51	EXPORT_SYMBOL(lockref_get);
	52
	53	/**
	54	* lockref_get_not_zero - Increments count unless the count is 0
	55	* @lockcnt: pointer to lockref structure
	56	* Return: 1 if count updated successfully or 0 if count was zero
	57	*/
	58	int lockref_get_not_zero(struct lockref *lockref)
	59	{
bc08b449 LT	60	int retval;
	61
	62	CMPXCHG_LOOP(
	63	new.count++;
	64	if (!old.count)
	65	return 0;
	66	,
	67	return 1;
	68	);
2f4f12e5 LT	69
2f4f12e5 LT	70	spin_lock(&lockref->lock);
bc08b449	71	retval = 0;
2f4f12e5 LT	72	if (lockref->count) {
	73	lockref->count++;
	74	retval = 1;
	75	}
	76	spin_unlock(&lockref->lock);
	77	return retval;
	78	}
	79	EXPORT_SYMBOL(lockref_get_not_zero);
	80
	81	/**
	82	* lockref_get_or_lock - Increments count unless the count is 0
	83	* @lockcnt: pointer to lockref structure
	84	* Return: 1 if count updated successfully or 0 if count was zero
	85	* and we got the lock instead.
	86	*/
	87	int lockref_get_or_lock(struct lockref *lockref)
	88	{
bc08b449 LT	89	CMPXCHG_LOOP(
	90	new.count++;
	91	if (!old.count)
	92	break;
	93	,
	94	return 1;
	95	);
	96
2f4f12e5 LT	97	spin_lock(&lockref->lock);
	98	if (!lockref->count)
	99	return 0;
	100	lockref->count++;
	101	spin_unlock(&lockref->lock);
	102	return 1;
	103	}
	104	EXPORT_SYMBOL(lockref_get_or_lock);
	105
	106	/**
	107	* lockref_put_or_lock - decrements count unless count <= 1 before decrement
	108	* @lockcnt: pointer to lockref structure
	109	* Return: 1 if count updated successfully or 0 if count <= 1 and lock taken
	110	*/
	111	int lockref_put_or_lock(struct lockref *lockref)
	112	{
bc08b449 LT	113	CMPXCHG_LOOP(
	114	new.count--;
	115	if (old.count <= 1)
	116	break;
	117	,
	118	return 1;
	119	);
	120
2f4f12e5 LT	121	spin_lock(&lockref->lock);
	122	if (lockref->count <= 1)
	123	return 0;
	124	lockref->count--;
	125	spin_unlock(&lockref->lock);
	126	return 1;
	127	}
	128	EXPORT_SYMBOL(lockref_put_or_lock);