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

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Message-ID: <20091011124616.GA4081@lst.de>
Date:	Sun, 11 Oct 2009 14:46:16 +0200
From:	Christoph Hellwig <hch@....de>
To:	John Kacur <jkacur@...hat.com>
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

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.

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