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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>
This commit is contained in:
Davidlohr Bueso 2016-04-20 20:09:24 -07:00 committed by Thomas Gleixner
parent 89e9e66ba1
commit fe1bce9e21
1 changed files with 1 additions and 1 deletions
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2
kernel/futex.c
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@ -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);