linux-kernel - Re: [PATCH 2.6.19 5/5] fs: freeze

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Date:	Tue, 7 Nov 2006 15:00:17 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Alasdair G Kergon <agk@...hat.com>, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, Ingo Molnar <mingo@...e.hu>,
	Srinivasa DS <srinivasa@...ibm.com>
Subject: Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex

On Tue, 07 Nov 2006 16:45:07 -0600
Eric Sandeen <sandeen@...hat.com> wrote:

> Andrew Morton wrote:
> 
> >> --- linux-2.6.19-rc4.orig/fs/buffer.c	2006-11-07 17:06:20.000000000 +0000
> >> +++ linux-2.6.19-rc4/fs/buffer.c	2006-11-07 17:26:04.000000000 +0000
> >> @@ -188,7 +188,9 @@ struct super_block *freeze_bdev(struct b
> >>  {
> >>  	struct super_block *sb;
> >>  
> >> -	mutex_lock(&bdev->bd_mount_mutex);
> >> +	if (down_trylock(&bdev->bd_mount_sem))
> >> +		return -EBUSY;
> >> +
> > 
> > This is a functional change which isn't described in the changelog.  What's
> > happening here?
> 
> Only allow one bdev-freezer in at a time, rather than queueing them up?
> 

You're asking me? ;)

Guys, I'm going to park this patch pending a full description of what it
does, a description of what the above hunk is doing and pending an
examination of whether we'd be better off changing the mutex-debugging code
rather than switching to semaphores.

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