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Re: bd_mount_mutex -> bd_mount_sem (was Re: xfs_file_ioctl / xfs_freeze:

To: Andrew Morton <akpm@xxxxxxxx>
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())
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 9 Jan 2007 10:04:20 +0000
Cc: Eric Sandeen <sandeen@xxxxxxxxxxx>, David Chinner <dgc@xxxxxxx>, linux-kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20070108195127.67fe86b8.akpm@xxxxxxxx>
Mail-followup-to: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxxx>, David Chinner <dgc@xxxxxxx>, linux-kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
References: <20070104001420.GA32440@xxxxxxxxxxxxxxx> <20070107213734.GS44411608@xxxxxxxxxxxxxxxxx> <20070108110323.GA3803@xxxxxxxxxxxxxxx> <45A27416.8030600@xxxxxxxxxxx> <20070108234728.GC33919298@xxxxxxxxxxxxxxxxx> <20070108161917.73a4c2c6.akpm@xxxxxxxx> <45A30828.6000508@xxxxxxxxxxx> <20070108191800.9d83ff5e.akpm@xxxxxxxx> <45A30E1D.4030401@xxxxxxxxxxx> <20070108195127.67fe86b8.akpm@xxxxxxxx>
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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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