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Commit b1fca266 authored by Eric Paris's avatar Eric Paris Committed by Ingo Molnar
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mutex: add atomic_dec_and_mutex_lock() 



Much like the atomic_dec_and_lock() function in which we take an hold a
spin_lock if we drop the atomic to 0 this function takes and holds the
mutex if we dec the atomic to 0.

Signed-off-by: default avatarEric Paris <eparis@redhat.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Orig-LKML-Reference: <20090323172417.410913479@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 56a50add

include/linux/mutex.h

+23 −0
Original line number Diff line number Diff line
@@ -151,4 +151,27 @@ extern int __must_check mutex_lock_killable(struct mutex *lock); 
extern int mutex_trylock(struct mutex *lock);

extern void mutex_unlock(struct mutex *lock);



/**

 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0

 * @cnt: the atomic which we are to dec

 * @lock: the mutex to return holding if we dec to 0

 *

 * return true and hold lock if we dec to 0, return false otherwise

 */

static inline int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)

{

	/* dec if we can't possibly hit 0 */

	if (atomic_add_unless(cnt, -1, 1))

		return 0;

	/* we might hit 0, so take the lock */

	mutex_lock(lock);

	if (!atomic_dec_and_test(cnt)) {

		/* when we actually did the dec, we didn't hit 0 */

		mutex_unlock(lock);

		return 0;

	}

	/* we hit 0, and we hold the lock */

	return 1;

}



#endif