[dm-devel] Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex
Rafael J. Wysocki
rjw at sisk.pl
Tue Nov 7 23:05:49 UTC 2006
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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