linux-kernel - Re: xfs_file_ioctl / xfs_freeze: BUG: warning at kernel/mutex-debug.c:80/debug_mutex

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Message-ID: <20070109064113.GB5569@elte.hu>
Date:	Tue, 9 Jan 2007 07:41:13 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...l.org>
Cc:	David Chinner <dgc@....com>,
	linux-kernel Mailing List <linux-kernel@...r.kernel.org>,
	xfs@....sgi.com, Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: xfs_file_ioctl / xfs_freeze: BUG: warning at kernel/mutex-debug.c:80/debug_mutex_unlock()


* Andrew Morton <akpm@...l.org> wrote:

> > Revert bd_mount_mutex back to a semaphore so that xfs_freeze -f 
> > /mnt/newtest; xfs_freeze -u /mnt/newtest works safely and doesn't 
> > produce lockdep warnings.
> 
> Sad.  The alternative would be to implement 
> mutex_unlock_dont_warn_if_a_different_task_did_it().  Ingo?  Possible?

i'd like to avoid it as much as i'd like to avoid having to add 
spin_unlock_dont_warn_if_a_different_task_did_it(). Unlocking by a 
different task is usually a sign of messy locking and bugs lurking. Is 
it really true that XFS's use of bd_mount_mutex is safe and justified?

	Ingo
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