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

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Date:	Wed, 10 Dec 2008 16:52:57 -0800
From:	Paul Menage <menage@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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, 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.

Paul
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