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

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Message-ID: <50811E5E.1090205@huawei.com>
Date:	Fri, 19 Oct 2012 17:33:18 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.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 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")

> We could theoretically call them outside of the
> lock but then we have to move after CGRP_REMOVED flag is set.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> ---
>  kernel/cgroup.c |   30 +++++++++---------------------
>  1 file changed, 9 insertions(+), 21 deletions(-)

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