linux-kernel - Re: [xfs-masters] INFO: possible circular locking dependency detected

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Date:	Sun, 11 Oct 2009 17:59:54 +0200 (CEST)
From:	John Kacur <jkacur@...hat.com>
To:	Christoph Hellwig <hch@....de>
cc:	linux-kernel@...r.kernel.org, xfs-masters@....sgi.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [xfs-masters] INFO: possible circular locking dependency
 detected



On Sun, 11 Oct 2009, Christoph Hellwig wrote:

> This has been around for a long time, the VM calls into fput and thus
> ->release with the mmap_sem held, which makes it really hard for a
> filesystem to avoid a lock inversion if it uses a lock both in ->release
> and the I/O path.
> 
> I have a workaround for this to only acquire the XFS iolock with a
> trylock in the release path and leave cleaning up stale preallocations
> until the final iput.  It's not pretty, but given that we're unlikely
> to see the VM fixed I might aswell finally send it for inclusion.
> 

In seems very easy and reliable to reproduce on my machine - so I am happy 
to test the patch here when you're ready.

Thanks

John
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