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Message-ID: <1347810587.13258.279.camel@deadeye.wl.decadent.org.uk>
Date: Sun, 16 Sep 2012 16:49:47 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: Tejun Heo <tj@...nel.org>
Cc: Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Subject: Re: [PATCH -stable] workqueue: UNBOUND -> REBIND morphing in
rebind_workers() should be atomic
On Tue, 2012-09-04 at 16:58 -0700, Tejun Heo wrote:
> From: Lai Jiangshan <laijs@...fujitsu.com>
>
> 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.
[...]
Added to the queue for 3.2, thanks.
Ben.
--
Ben Hutchings
Experience is what causes a person to make new mistakes instead of old ones.
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