From: Tejun Heo <tj@kernel.org>
Date: Tue, 13 Dec 2011 02:12:21 +0000 (-0800)
Subject: cgroup: add cgroup_root_mutex
X-Git-Tag: v3.3-rc1~148^2~20
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e25e2cbb4c6679bed5f52fb0f2cc381688297901;p=pandora-kernel.git

cgroup: add cgroup_root_mutex

cgroup wants to make threadgroup stable while modifying cgroup
hierarchies which will introduce locking dependency on
cred_guard_mutex from cgroup_mutex.  This unfortunately completes
circular dependency.

 A. cgroup_mutex -> cred_guard_mutex -> s_type->i_mutex_key -> namespace_sem
 B. namespace_sem -> cgroup_mutex

B is from cgroup_show_options() and this patch breaks it by
introducing another mutex cgroup_root_mutex which nests inside
cgroup_mutex and protects cgroupfs_root.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
---

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