Subject: Re: [ckrm-tech] Circular Locking Dependency Chain detected in
	containers code
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Paul Menage <menage@google.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>, linux-kernel@vger.kernel.org,
       akpm@linux-foundation.com,
       Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
       ckrm-tech@lists.sourceforge.net
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References: <20070807062600.GH31148@linux.vnet.ibm.com>
	 <6599ad830708071310i4fa7a98age169e2d650421d8b@mail.gmail.com>
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Date: Tue, 07 Aug 2007 22:23:28 +0200
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On Tue, 2007-08-07 at 13:10 -0700, Paul Menage wrote:
> I'm away from work at the moment and can't investigate fully, but it
> looks as though this may be the same one that I mentioned in the
> introductory email to the patchset. If so, it's a false positive -
> there's a point in the container mount code where we need to lock a
> newly-created (and hence guaranteed unlocked) directory inode while
> holding container mutex. This makes the lockdep code think that
> inode->i_mutex nests inside container_mutex, when in fact
> container_mutex nests outside inode->i_mutex in all cases except this
> one case where i_mutex can't possibly be locked.
> 
> I've not learned enough about lockdep yet to figure out how to shut it
> up in this case.

The typical annotation would be using spin_lock_nested/mutex_lock_nested
with a non-0 nesting level for this one case.

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