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

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Message-ID: <20061110103942.GG3196@elf.ucw.cz>
Date:	Fri, 10 Nov 2006 11:39:42 +0100
From:	Pavel Machek <pavel@....cz>
To:	David Chinner <dgc@....com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alasdair G Kergon <agk@...hat.com>,
	Eric Sandeen <sandeen@...hat.com>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, Srinivasa DS <srinivasa@...ibm.com>,
	Nigel Cunningham <nigel@...pend2.net>
Subject: Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex

On Fri 2006-11-10 11:57:49, David Chinner wrote:
> On Thu, Nov 09, 2006 at 11:21:46PM +0100, Rafael J. Wysocki wrote:
> > I think we can add a flag to __create_workqueue() that will indicate if
> > this one is to be running with PF_NOFREEZE and a corresponding macro like
> > create_freezable_workqueue() to be used wherever we want the worker thread
> > to freeze (in which case it should be calling try_to_freeze() somewhere).
> > Then, we can teach filesystems to use this macro instead of
> > create_workqueue().
> 
> At what point does the workqueue get frozen? i.e. how does this
> guarantee an unfrozen filesystem will end up in a consistent
> state?

Snapshot is atomic; workqueue will be unfrozen with everyone else, but
as there were no writes in the meantime, there should be no problems.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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