linux-kernel - Re: [RFC][PATCH 2/3] CGroups: Use hierarchy

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Date:	Thu, 11 Dec 2008 12:03:07 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Paul Menage <menage@...gle.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [RFC][PATCH 2/3] CGroups: Use hierarchy_mutex in memory
	controller

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2008-12-11 10:05:01]:

> On Wed, 10 Dec 2008 16:52:57 -0800
> Paul Menage <menage@...gle.com> wrote:
> 
> > On Wed, Dec 10, 2008 at 4:49 PM, KAMEZAWA Hiroyuki
> > <kamezawa.hiroyu@...fujitsu.com> wrote:
> > >
> > >        an operation like rmdir() in somewhere.
> > >                hierarchy_lock for A (acquired)
> > >                hierarchy_lock for B (waiting)
> > >
> > >        in subsys A.
> > >                mmap_sem (acquired)
> > >                hierarchy_lock for A (waiting)
> > >        in subsys B.
> > >                hierarchy_lock for B (aquired)
> > >                mmap_sem             (waiting)
> > >
> > 
> > That's a valid deadlock - you'd need to require the mmap_sem nests
> > either inside all hierarchy_mutexes or else outside all of them.
> > 
> This was a found dead lock between memcg and cpuset.
> 
> another one was 
> 
> 	an operation like rmdir() in somewhere.
> 		hierarchy_lock for memcg (acquired)
> 		hierarchy_lock for B (waiting)
> 
> 	in subsys B.
> 		hierarchy_lock for B (aquired)

But then the hierarchy_locks acquired will be different right?

> 		have to do some memory reclaim -> hierarchy_lock for memcg (waiting)
> 
> I have no objections to hierarchy_lock itself but calling context to memcg is very
> complicated and simple replace of these locks will be just a small help.

Could you please explain the race better?

-- 
	Balbir
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