Patch "futex: Acknowledge a new waiter in counter before plist" has been added to the 4.4-stable tree

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

futex: Acknowledge a new waiter in counter before plist

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
futex-acknowledge-a-new-waiter-in-counter-before-plist.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 <[email protected]> know about it.

From: Davidlohr Bueso <[email protected]>
Date: Wed, 20 Apr 2016 20:09:24 -0700
Subject: futex: Acknowledge a new waiter in counter before plist

From: Davidlohr Bueso <[email protected]>

commit fe1bce9e2107ba3a8faffe572483b6974201a0e6 upstream.

Otherwise an incoming waker on the dest hash bucket can miss the waiter adding itself to the plist during the lockless check optimization (small window but still the correct way of doing this); similarly to the decrement counterpart.

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

@@ -1484,8 +1484,8 @@ void requeue_futex(struct futex_q *q, st
 	if (likely(&hb1->chain != &hb2->chain)) {
 		plist_del(&q->list, &hb1->chain);
 		hb_waiters_dec(hb1);
-		plist_add(&q->list, &hb2->chain);
 		hb_waiters_inc(hb2);
+		plist_add(&q->list, &hb2->chain);
 		q->lock_ptr = &hb2->lock;
 	}
 	get_futex_key_refs(key2);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/futex-handle-unlock_pi-race-gracefully.patch queue-4.4/futex-acknowledge-a-new-waiter-in-counter-before-plist.patch