linux-kernel - Re: bd_mount_mutex -> bd_mount_sem (was Re: xfs_file_ioctl / xfs_freeze: BUG: warning at kernel/mutex-debug.c:80/debug_mutex

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Message-ID: <20070109100420.GB14713@infradead.org>
Date:	Tue, 9 Jan 2007 10:04:20 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	Andrew Morton <akpm@...l.org>
Cc:	Eric Sandeen <sandeen@...deen.net>, David Chinner <dgc@....com>,
	linux-kernel Mailing List <linux-kernel@...r.kernel.org>,
	xfs@....sgi.com
Subject: Re: bd_mount_mutex -> bd_mount_sem (was Re: xfs_file_ioctl / xfs_freeze: BUG: warning at kernel/mutex-debug.c:80/debug_mutex_unlock())

On Mon, Jan 08, 2007 at 07:51:27PM -0800, Andrew Morton wrote:
> I don't even know what code we're talking about here...
> 
> I'm under the impression that XFS will return to userspace with a
> filesystem lock held, under the expectation (ie: requirement) that
> userspace will later come in and release that lock.
> 
> If that's not true, then what _is_ happening in there?
> 
> If that _is_ true then, well, that sucks a bit.

It's not a filesystem lock.  It's a per-blockdevice lock that prevents
multiple people from freezing the filesystem at the same time, aswell
as providing exclusion between a frozen filesystem an mount-related
activity.  It's a traditional text-box example for a semaphore.
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