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

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Date:	Sun, 12 Nov 2006 18:43:10 +0000
From:	Pavel Machek <pavel@...e.cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	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>,
	David Chinner <dgc@....com>
Subject: Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex

Hi!

> > Okay, so you claim that sys_sync can stall, waiting for administator?
> > 
> > In such case we can simply do one sys_sync() before we start freezing
> > userspace... or just more the only sys_sync() there. That way, admin
> > has chance to unlock his system.
> 
> Well, this is a different story.
> 
> My point is that if we call sys_sync() _anyway_ before calling
> freeze_filesystems(), then freeze_filesystems() is _safe_ (either the
> sys_sync() blocks, or it doesn't in which case freeze_filesystems() won't
> block either).
> 
> This means, however, that we can leave the patch as is (well, with the minor
> fix I have already posted), for now, because it doesn't make things worse a
> bit, but:
> (a) it prevents xfs from being corrupted and

I'd really prefer it to be fixed by 'freezeable workqueues'. Can you
point me into sources -- which xfs workqueues are problematic?

(It would be nice to fix that for 2.6.19, and full bdev freezing looks
intrusive to me).

> (b) it prevents journaling filesystems in general from replaying journals
> after a failing resume.

I do not see b) as an useful goal.
							Pavel

-- 
Thanks for all the (sleeping) penguins.
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