This is a note to let you know that I've just added the patch titled

locking/mutex: Allow next waiter lockless wakeup

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: locking-mutex-allow-next-waiter-lockless-wakeup.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 1329ce6fbbe4536592dfcfc8d64d61bfeb598fe6 Mon Sep 17 00:00:00 2001

From: Davidlohr Bueso dave@stgolabs.net Date: Sun, 24 Jan 2016 18:23:43 -0800 Subject: locking/mutex: Allow next waiter lockless wakeup

From: Davidlohr Bueso dave@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.Long@hpe.com Signed-off-by: Davidlohr Bueso dbueso@suse.de Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Ding Tianhong dingtianhong@huawei.com Cc: Jason Low jason.low2@hp.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Paul E. McKenney paulmck@linux.vnet.ibm.com Cc: Paul E. McKenney paulmck@us.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Waiman Long waiman.long@hpe.com Cc: Will Deacon Will.Deacon@arm.com Link: http://lkml.kernel.org/r/20160125022343.GA3322@linux-uzut.site Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@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); }

/*

Patches currently in stable-queue which might be from dave@stgolabs.net are

queue-4.4/locking-mutex-allow-next-waiter-lockless-wakeup.patch queue-4.4/futex-replace-barrier-in-unqueue_me-with-read_once.patch