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

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Date:	Thu, 11 Dec 2008 10:05:01 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Paul Menage <menage@...gle.com>
Cc:	balbir@...ux.vnet.ibm.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

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)
		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.

-Kame

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