Re: [tip:sched/core] sched: Fix race in task_group()

From: cwillu
Date: Thu Oct 18 2012 - 04:27:07 EST

On Tue, Jul 24, 2012 at 8:21 AM, tip-bot for Peter Zijlstra
<peterz@xxxxxxxxxxxxx> wrote:
> Commit-ID: 8323f26ce3425460769605a6aece7a174edaa7d1
> Gitweb:
> Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> AuthorDate: Fri, 22 Jun 2012 13:36:05 +0200
> Committer: Ingo Molnar <mingo@xxxxxxxxxx>
> 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@xxxxxxxxxxxxx>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Link:
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>

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):
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