linux-kernel - Re: [ckrm-tech] Circular Locking Dependency Chain detected in containers code

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Date:	Tue, 07 Aug 2007 22:23:28 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Menage <menage@...gle.com>
Cc:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.com,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	ckrm-tech@...ts.sourceforge.net
Subject: Re: [ckrm-tech] Circular Locking Dependency Chain detected in
	containers code

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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