Commit b1fca266 authored by Eric Paris's avatar Eric Paris Committed by Ingo Molnar

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
......@@ -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
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