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[PATCH] Fix memory ordering problem in wake_futex()

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Fix a memory ordering problem that occurs on IA64. The "store" to q->lock_ptr
in wake_futex() can become visible before wake_up_all() clears the lock in the
futex_q.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Andrew Morton 2005-12-23 19:54:46 -08:00 committed by Linus Torvalds
parent 6003a93e7b
commit 8e31108b9f
1 changed files with 6 additions and 0 deletions
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6
kernel/futex.c
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@ -270,7 +270,13 @@ static void wake_futex(struct futex_q *q)
/*
* The waiting task can free the futex_q as soon as this is written,
* without taking any locks. This must come last.
*
* A memory barrier is required here to prevent the following store
* to lock_ptr from getting ahead of the wakeup. Clearing the lock
* at the end of wake_up_all() does not prevent this store from
* moving.
*/
wmb();
q->lock_ptr = NULL;
}