From: Lai Jiangshan <laijs@cn.fujitsu.com>
Date: Sat, 1 Sep 2012 16:28:19 +0000 (+0800)
Subject: workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic
X-Git-Tag: v3.2.30~60
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f152c392a7715862818fb671cbd5e0b2545aedae;p=pandora-kernel.git

workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic

commit 96e65306b81351b656835c15931d1d237b252f27 upstream.

The compiler may compile the following code into TWO write/modify
instructions.

	worker->flags &= ~WORKER_UNBOUND;
	worker->flags |= WORKER_REBIND;

so the other CPU may temporarily see worker->flags which doesn't have
either WORKER_UNBOUND or WORKER_REBIND set and perform local wakeup
prematurely.

Fix it by using single explicit assignment via ACCESS_ONCE().

Because idle workers have another WORKER_NOT_RUNNING flag, this bug
doesn't exist for them; however, update it to use the same pattern for
consistency.

tj: Applied the change to idle workers too and updated comments and
    patch description a bit.

stable: Idle worker rebinding doesn't apply for -stable and
        WORKER_UNBOUND used to be WORKER_ROGUE.  Updated accordingly.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---

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