From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 22 Jun 2012 11:36:05 +0000 (+0200)
Subject: sched: Fix race in task_group()
X-Git-Tag: v3.2.27~70
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b75bfc42974aaf089ae7eae5d3c6bf362f57ee93;p=pandora-kernel.git

sched: Fix race in task_group()

commit 8323f26ce3425460769605a6aece7a174edaa7d1 upstream

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@canonical.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1340364965.18025.71.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>

(backported to previous file names and layout)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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