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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Date:	Mon, 8 Jan 2007 19:51:27 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Eric Sandeen <sandeen@...deen.net>
Cc:	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, 08 Jan 2007 21:38:05 -0600
Eric Sandeen <sandeen@...deen.net> wrote:

> Andrew Morton wrote:
> > On Mon, 08 Jan 2007 21:12:40 -0600
> > Eric Sandeen <sandeen@...deen.net> wrote:
> > 
> >> Andrew Morton wrote:
> >>> On Tue, 9 Jan 2007 10:47:28 +1100
> >>> David Chinner <dgc@....com> wrote:
> >>>
> >>>> On Mon, Jan 08, 2007 at 10:40:54AM -0600, Eric Sandeen wrote:
> >>>>> Sami Farin wrote:
> >>>>>> On Mon, Jan 08, 2007 at 08:37:34 +1100, David Chinner wrote:
> >>>>>> ...
> >>>>>>>> fstab was there just fine after -u.
> >>>>>>> Oh, that still hasn't been fixed?
> >>>>>> Looked like it =)
> >>>>> Hm, it was proposed upstream a while ago:
> >>>>>
> >>>>> http://lkml.org/lkml/2006/9/27/137
> >>>>>
> >>>>> I guess it got lost?
> >>>> Seems like it. Andrew, did this ever get queued for merge?
> >>> Seems not.  I think people were hoping that various nasties in there
> >>> would go away.  We return to userspace with a kernel lock held??
> >> Is a semaphore any worse than the current mutex in this respect?  At 
> >> least unlocking from another thread doesn't violate semaphore rules.  :)
> > 
> > I assume that if we weren't returning to userspace with a lock held, this
> > mutex problem would simply go away.
> > 
> 
> Well nobody's asserting that the filesystem must always be locked & 
> unlocked by the same thread, are they?  That'd be a strange rule to 
> enforce upon the userspace doing the filesystem management wouldn't it? 
>   Or am I thinking about this wrong...

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.
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