locking/mutexes: Document quick lock release when unlocking (42fa566b) · Commits · e / devices / android_kernel_fairphone_FP5

When unlocking, we always want to reach the slowpath with the lock's counter indicating it is unlocked. -- as returned by the asm fastpath call or by explicitly setting it. While doing so, at least in theory, we can optimize and allow faster lock stealing. When unlocking, we always want to reach the slowpath with the lock's counter indicating it is unlocked. -- as returned by the asm fastpath call or by explicitly setting it. While doing so, at least in theory, we can optimize and allow faster lock stealing. Signed-off-by:

Davidlohr Bueso <davidlohr@hp.com> Signed-off-by:

Peter Zijlstra <peterz@infradead.org> Cc: jason.low2@hp.com Cc: aswin@hp.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1406752916-3341-2-git-send-email-davidlohr@hp.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/locking/mutex.c

+9 −2

Original line number	Original line	Diff line number	Diff line
	@@ -684,9 +684,16 @@ __mutex_unlock_common_slowpath(struct mutex *lock, int nested)
	unsigned long flags;		unsigned long flags;

	/*		/*
	* some architectures leave the lock unlocked in the fastpath failure		* As a performance measurement, release the lock before doing other
			* wakeup related duties to follow. This allows other tasks to acquire
			* the lock sooner, while still handling cleanups in past unlock calls.
			* This can be done as we do not enforce strict equivalence between the
			* mutex counter and wait_list.
			*
			*
			* Some architectures leave the lock unlocked in the fastpath failure
	* case, others need to leave it locked. In the later case we have to		* case, others need to leave it locked. In the later case we have to
	* unlock it here		* unlock it here - as the lock counter is currently 0 or negative.
	*/		*/
	if (__mutex_slowpath_needs_to_unlock())		if (__mutex_slowpath_needs_to_unlock())
	atomic_set(&lock->count, 1);		atomic_set(&lock->count, 1);