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

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Message-ID: <20121019201736.GQ13370@google.com>
Date:	Fri, 19 Oct 2012 13:17:36 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>
Subject: Re: [PATCH 4/6] cgroups: forbid pre_destroy callback to fail

On Fri, Oct 19, 2012 at 05:33:18PM +0800, Li Zefan wrote:
> On 2012/10/17 21:30, Michal Hocko wrote:
> > Now that mem_cgroup_pre_destroy callback doesn't fail 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.
> 
> > The callbacks are also called from within cgroup_lock to guarantee that
> > no new tasks show up. 
> 
> I'm afraid this won't work. See commit 3fa59dfbc3b223f02c26593be69ce6fc9a940405
> ("cgroup: fix potential deadlock in pre_destroy")

Yeah, you're right.  Argh... we really should unexport cgroup_lock
soon.

Thanks.

-- 
tejun
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