Commit fe1bce9e authored Apr 20, 2016 by Davidlohr Bueso Committed by Thomas Gleixner Apr 21, 2016

futex: Acknowledge a new waiter in counter before plist



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.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: bigeasy@linutronix.de
Cc: dvhart@infradead.org
Cc: stable@kernel.org
Link: http://lkml.kernel.org/r/1461208164-29150-1-git-send-email-dave@stgolabs.net


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

parent 89e9e66b

kernel/futex.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1535,8 +1535,8 @@ void requeue_futex(struct futex_q q, struct futex_hash_bucket hb1,
		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);

Admin message