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Date: Wed, 23 Jan 2008 12:55:04 +0000
From: Christoph Hellwig <hch@infradead.org>
To: David Chinner <dgc@sgi.com>
Cc: Jonathan Woithe <jwoithe@physics.adelaide.edu.au>,
       linux-kernel@vger.kernel.org
Subject: Re: do_remount_sb(RDONLY) race? (was: XFS oops under 2.6.23.9)
Message-ID: <20080123125504.GC25395@infradead.org>
References: <200801230430.m0N4UmpU029430@turbo.physics.adelaide.edu.au> <20080123053412.GN155259@sgi.com>
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On Wed, Jan 23, 2008 at 04:34:12PM +1100, David Chinner wrote:
> I've had suspicions of a race in the remount-ro code in
> do_remount_sb() w.r.t to the fs_may_remount_ro() check.  That is, we
> do an unlocked check to see if we can remount readonly and then fail
> to check again once we've locked the superblock out and start the
> remount.

This code is inherently racy, and will be replaced with a proper
per-vfsmount writer count in 2.6.25 as part of the per-mount r/o patches.