linux-kernel - Re: [PATCH] cgroup: use an ordered workqueue for cgroup destruction

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Message-ID: <20140207152158.GC3304@htj.dyndns.org>
Date:	Fri, 7 Feb 2014 10:21:58 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Filipe Brandenburger <filbranden@...gle.com>,
	Li Zefan <lizefan@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Markus Blank-Burian <burian@...nster.de>,
	Shawn Bohrer <shawn.bohrer@...il.com>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] cgroup: use an ordered workqueue for cgroup destruction

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@...gle.com>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> Cc: stable@...r.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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