linux-kernel - Re: [PATCH 01/10] cgroup: add cgroup_root

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Message-Id: <20111104173834.ea089a41.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 4 Nov 2011 17:38:34 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	paul@...lmenage.org, rjw@...k.pl, lizf@...fujitsu.com,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, fweisbec@...il.com,
	matthltc@...ibm.com, akpm@...ux-foundation.org, oleg@...hat.com,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 01/10] cgroup: add cgroup_root_mutex

On Tue,  1 Nov 2011 16:46:24 -0700
Tejun Heo <tj@...nel.org> wrote:

> 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@...nel.org>
> Cc: Oleg Nesterov <oleg@...hat.com>

Thanks,
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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