linux-kernel - Re: [RFC][RFT] memcg fix cgroup_mutex deadlock when cpuset reclaims memory

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Message-ID: <20081210074611.GA25467@balbir.in.ibm.com>
Date:	Wed, 10 Dec 2008 13:16:11 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	menage@...gle.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyuki@...fujitsu.com>,
	Daisuke Miyakawa <dmiyakawa@...gle.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][RFT] memcg fix cgroup_mutex deadlock when cpuset
	reclaims memory

* Daisuke Nishimura <nishimura@....nes.nec.co.jp> [2008-12-10 15:19:48]:

> On Wed, 10 Dec 2008 10:49:47 +0530, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> > Hi,
> > 
> > Here is a proposed fix for the memory controller cgroup_mutex deadlock
> > reported. It is lightly tested and reviewed. I need help with review
> > and test. Is the reported deadlock reproducible after this patch? A
> > careful review of the cpuset impact will also be highly appreciated.
> > 
> > From: Balbir Singh <balbir@...ux.vnet.ibm.com>
> > 
> > cpuset_migrate_mm() holds cgroup_mutex throughout the duration of
> > do_migrate_pages(). The issue with that is that
> > 
> > 1. It can lead to deadlock with memcg, as do_migrate_pages()
> >    enters reclaim
> > 2. It can lead to long latencies, preventing users from creating/
> >    destroying other cgroups anywhere else
> > 
> > The patch holds callback_mutex through the duration of cpuset_migrate_mm() and
> > gives up cgroup_mutex while doing so.
> > 
> I agree changing cpuset_migrate_mm not to hold cgroup_mutex to fix the dead lock
> is one choice, and it looks good to me at the first impression.
> 
> But I'm not sure it's good to change cpuset(other subsystem) code because of memcg.
> 
> Anyway, I'll test this patch and report the result tomorrow.
> (Sorry, I don't have enough time today.)

Thanks for helping Daisuke-San!

I'll look forward to your test result. I'll continue to pound my
system meanwhile

-- 
	Balbir
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