mutex: add atomic_dec_and_mutex_lock() (9ab772cd) · Commits · 戴 / test

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:

Eric Paris <eparis@redhat.com> Signed-off-by:

Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Paul Mackerras <paulus@samba.org> Orig-LKML-Reference: <20090323172417.410913479@chello.nl> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

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

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