4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Davidlohr Bueso <d...@stgolabs.net> commit 1329ce6fbbe4536592dfcfc8d64d61bfeb598fe6 upstream. Make use of wake-queues and enable the wakeup to occur after releasing the wait_lock. This is similar to what we do with rtmutex top waiter, slightly shortening the critical region and allow other waiters to acquire the wait_lock sooner. In low contention cases it can also help the recently woken waiter to find the wait_lock available (fastpath) when it continues execution. Reviewed-by: Waiman Long <waiman.l...@hpe.com> Signed-off-by: Davidlohr Bueso <dbu...@suse.de> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Andrew Morton <a...@linux-foundation.org> Cc: Ding Tianhong <dingtianh...@huawei.com> Cc: Jason Low <jason.l...@hp.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com> Cc: Paul E. McKenney <paul...@us.ibm.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: Tim Chen <tim.c.c...@linux.intel.com> Cc: Waiman Long <waiman.l...@hpe.com> Cc: Will Deacon <will.dea...@arm.com> Link: http://lkml.kernel.org/r/20160125022343.ga3...@linux-uzut.site Signed-off-by: Ingo Molnar <mi...@kernel.org> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- kernel/locking/mutex.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -719,6 +719,7 @@ static inline void __mutex_unlock_common_slowpath(struct mutex *lock, int nested) { unsigned long flags; + WAKE_Q(wake_q); /* * As a performance measurement, release the lock before doing other @@ -746,11 +747,11 @@ __mutex_unlock_common_slowpath(struct mu struct mutex_waiter, list); debug_mutex_wake_waiter(lock, waiter); - - wake_up_process(waiter->task); + wake_q_add(&wake_q, waiter->task); } spin_unlock_mutex(&lock->wait_lock, flags); + wake_up_q(&wake_q); } /*
