From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] cgroup: use an ordered workqueue for cgroup destruction
Date: Fri, 7 Feb 2014 10:21:58 -0500
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To: Hugh Dickins <hughd@google.com>
Cc: Filipe Brandenburger <filbranden@google.com>, Li Zefan <lizefan@huawei.com>, Andrew Morton <akpm@linux-foundation.org>, Michal Hocko <mhocko@suse.cz>, Johannes Weiner <hannes@cmpxchg.org>, Greg Thelen <gthelen@google.com>, Michel Lespinasse <walken@google.com>, Markus Blank-Burian <burian@muenster.de>, Shawn Bohrer <shawn.bohrer@gmail.com>, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org

On Thu, Feb 06, 2014 at 03:56:01PM -0800, Hugh Dickins wrote:
> Sometimes the cleanup after memcg hierarchy testing gets stuck in
> mem_cgroup_reparent_charges(), unable to bring non-kmem usage down to 0.
> 
> There may turn out to be several causes, but a major cause is this: the
> workitem to offline parent can get run before workitem to offline child;
> parent's mem_cgroup_reparent_charges() circles around waiting for the
> child's pages to be reparented to its lrus, but it's holding cgroup_mutex
> which prevents the child from reaching its mem_cgroup_reparent_charges().
> 
> Just use an ordered workqueue for cgroup_destroy_wq.
> 
> Fixes: e5fca243abae ("cgroup: use a dedicated workqueue for cgroup destruction")
> Suggested-by: Filipe Brandenburger <filbranden@google.com>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> Cc: stable@vger.kernel.org # 3.10+

Applied to cgroup/for-3.14-fixes with comment updated to indicate that
this is temporary.

Thanks.

-- 
tejun

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