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

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Date:	Wed, 8 Nov 2006 00:05:49 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Andrew Morton <akpm@...l.org>, 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 Tuesday, 7 November 2006 23:45, Eric Sandeen 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?

But freeze_bdev() is supposed to return the result of get_super(bdev)
_unconditionally_.  Moreover, in its current form freeze_bdev() _cannot_
_fail_, so I don't see how this change doesn't break any existing code.

For example freeze_filesystems() (recently added to -mm) will be broken
if the down_trylock() is unsuccessful.

Greetings,
Rafael


-- 
You never change things by fighting the existing reality.
		R. Buckminster Fuller
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