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

sched/wait: Fix add_wait_queue() behavioral change

to the 4.14-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: sched-wait-fix-add_wait_queue-behavioral-change.patch and it can be found in the queue-4.14 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 c6b9d9a33029014446bd9ed84c1688f6d3d4eab9 Mon Sep 17 00:00:00 2001

From: Omar Sandoval osandov@fb.com Date: Tue, 5 Dec 2017 23:15:31 -0800 Subject: sched/wait: Fix add_wait_queue() behavioral change

From: Omar Sandoval osandov@fb.com

commit c6b9d9a33029014446bd9ed84c1688f6d3d4eab9 upstream.

The following cleanup commit:

50816c48997a ("sched/wait: Standardize internal naming of wait-queue entries")

... unintentionally changed the behavior of add_wait_queue() from inserting the wait entry at the head of the wait queue to the tail of the wait queue.

Beyond a negative performance impact this change in behavior theoretically also breaks wait queues which mix exclusive and non-exclusive waiters, as non-exclusive waiters will not be woken up if they are queued behind enough exclusive waiters.

Signed-off-by: Omar Sandoval osandov@fb.com Reviewed-by: Jens Axboe axboe@kernel.dk Acked-by: Peter Zijlstra peterz@infradead.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Thomas Gleixner tglx@linutronix.de Cc: kernel-team@fb.com Fixes: ("sched/wait: Standardize internal naming of wait-queue entries") Link: http://lkml.kernel.org/r/a16c8ccffd39bd08fdaa45a5192294c784b803a7.1512544324... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- kernel/sched/wait.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -27,7 +27,7 @@ void add_wait_queue(struct wait_queue_he

wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE; spin_lock_irqsave(&wq_head->lock, flags); - __add_wait_queue_entry_tail(wq_head, wq_entry); + __add_wait_queue(wq_head, wq_entry); spin_unlock_irqrestore(&wq_head->lock, flags); } EXPORT_SYMBOL(add_wait_queue);

Patches currently in stable-queue which might be from osandov@fb.com are

queue-4.14/sched-wait-fix-add_wait_queue-behavioral-change.patch