linux-kernel - Re: [PATCH resend 3/3] vmpressure: Make sure there are no events queued after memcg is offlined

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Message-ID: <20130723161825.GC21100@mtj.dyndns.org>
Date:	Tue, 23 Jul 2013 12:18:25 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Li Zefan <lizefan@...wei.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH resend 3/3] vmpressure: Make sure there are no events
 queued after memcg is offlined

On Fri, Jul 19, 2013 at 06:51:11PM +0200, Michal Hocko wrote:
> vmpressure is called synchronously from the reclaim where the
> target_memcg is guaranteed to be alive but the eventfd is signaled from
> the work queue context. This means that memcg (along with vmpressure
> structure which is embedded into it) might go away while the work item
> is pending which would result in use-after-release bug.
> 
> We have two possible ways how to fix this. Either vmpressure pins memcg
> before it schedules vmpr->work and unpin it in vmpressure_work_fn or
> explicitely flush the work item from the css_offline context (as
> suggested by Tejun).
> 
> This patch implements the later one and it introduces vmpressure_cleanup
> which flushes the vmpressure work queue item item. It hooks into
> mem_cgroup_css_offline after the memcg itself is cleaned up.
> 
> Reported-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks!

-- 
tejun
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