linux-kernel - Re: [PATCH v3 4/6] cgroups: forbid pre

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Message-ID: <20121113211324.GC1543@cmpxchg.org>
Date:	Tue, 13 Nov 2012 16:13:24 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>,
	Glauber Costa <glommer@...allels.com>
Subject: Re: [PATCH v3 4/6] cgroups: forbid pre_destroy callback to fail

On Fri, Oct 26, 2012 at 01:37:31PM +0200, Michal Hocko wrote:
> Now that mem_cgroup_pre_destroy callback doesn't fail (other than a race
> with a task attach resp. child group appears) finally we can safely move
> on and forbit all the callbacks to fail.
> The last missing piece is moving cgroup_call_pre_destroy after
> cgroup_clear_css_refs so that css_tryget fails so no new charges for the
> memcg can happen.
> We cannot, however, move cgroup_call_pre_destroy right after because we
> cannot call mem_cgroup_pre_destroy with the cgroup_lock held (see
> 3fa59dfb cgroup: fix potential deadlock in pre_destroy) so we have to
> move it after the lock is released.
> 
> Changes since v1
> - Li Zefan pointed out that mem_cgroup_pre_destroy cannot be called with
>   cgroup_lock held
> 
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

Acked-by: Johannes Weiner <hannes@...xchg.org>
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