[dm-devel] Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex

[Alasdair G Kergon <agk redhat com>]

On Wed, Nov 08, 2006 at 12:05:49AM +0100, Rafael J. Wysocki wrote:
> 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.
 
I hadn't noticed that -mm patch.  I'll take a look.  Up to now, device-mapper
(via dmsetup) and xfs (via xfs_freeze, which dates from before device-mapper
handled this automatically) were the only users.  Only one freeze should be
issued at once.  A freeze is a temporary thing, normally used while creating a
snapshot.  (One problem we still have is lots of old documentation on the web
advising people to run xfs_freeze before creating device-mapper snapshots.)

You're right that the down_trylock idea is more trouble than it's worth and
should be scrapped.

Alasdair
-- 
agk redhat com