From: Tejun Heo <tj@kernel.org>
Date: Thu, 13 Feb 2014 18:29:31 +0000 (-0500)
Subject: cgroup: update cgroup_enable_task_cg_lists() to grab siglock
X-Git-Tag: v3.2.56~71
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a320419451b152ce343bd59675a5bfa0beffe9e9;p=pandora-kernel.git

cgroup: update cgroup_enable_task_cg_lists() to grab siglock

commit 532de3fc72adc2a6525c4d53c07bf81e1732083d upstream.

Currently, there's nothing preventing cgroup_enable_task_cg_lists()
from missing set PF_EXITING and race against cgroup_exit().  Depending
on the timing, cgroup_exit() may finish with the task still linked on
css_set leading to list corruption.  Fix it by grabbing siglock in
cgroup_enable_task_cg_lists() so that PF_EXITING is guaranteed to be
visible.

This whole on-demand cg_list optimization is extremely fragile and has
ample possibility to lead to bugs which can cause things like
once-a-year oops during boot.  I'm wondering whether the better
approach would be just adding "cgroup_disable=all" handling which
disables the whole cgroup rather than tempting fate with this
on-demand craziness.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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