linux-kernel - Re: [tip:sched/core] sched: Fix race in task

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Message-ID: <CAE5mzvjPXAZdOi1p8AB47zOQzgAErBU66gAS8spnpOs+=-+azA@mail.gmail.com>
Date:	Thu, 18 Oct 2012 02:27:10 -0600
From:	cwillu <cwillu@...llu.com>
To:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, peterz@...radead.org, tglx@...utronix.de,
	stefan.bader@...onical.com
Subject: Re: [tip:sched/core] sched: Fix race in task_group()

On Tue, Jul 24, 2012 at 8:21 AM, tip-bot for Peter Zijlstra
<peterz@...radead.org> wrote:
> Commit-ID:  8323f26ce3425460769605a6aece7a174edaa7d1
> Gitweb:     http://git.kernel.org/tip/8323f26ce3425460769605a6aece7a174edaa7d1
> Author:     Peter Zijlstra <peterz@...radead.org>
> AuthorDate: Fri, 22 Jun 2012 13:36:05 +0200
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Tue, 24 Jul 2012 13:58:20 +0200
>
> sched: Fix race in task_group()
>
> Stefan reported a crash on a kernel before a3e5d1091c1 ("sched:
> Don't call task_group() too many times in set_task_rq()"), he
> found the reason to be that the multiple task_group()
> invocations in set_task_rq() returned different values.
>
> Looking at all that I found a lack of serialization and plain
> wrong comments.
>
> The below tries to fix it using an extra pointer which is
> updated under the appropriate scheduler locks. Its not pretty,
> but I can't really see another way given how all the cgroup
> stuff works.
>
> Reported-and-tested-by: Stefan Bader <stefan.bader@...onical.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Link: http://lkml.kernel.org/r/1340364965.18025.71.camel@twins
> Signed-off-by: Ingo Molnar <mingo@...nel.org>

I just finished bisecting a crash on boot to this commit; booting with
"noautogroup" brings it back.

3.5.4 is the latest -stable that still boots, and none of the 3.6 rc's
boot at all.

Photo of the bug (3.6.0next is 3.6 + btrfs's for-linus):
https://lh5.googleusercontent.com/-0DY-YYhgvzs/UHdB-BQdzMI/AAAAAAAAAEg/QhY9rgxnv98/s811/2012-10-11
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