linux-kernel - Re: [PATCH] Freeze bdevs when freezing processes.

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Date:	Wed, 25 Oct 2006 02:33:45 +1000
From:	David Chinner <dgc@....com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	David Chinner <dgc@....com>,
	Nigel Cunningham <ncunningham@...uxmail.org>,
	Andrew Morton <akpm@...l.org>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	xfs@....sgi.com
Subject: Re: [PATCH] Freeze bdevs when freezing processes.

On Tue, Oct 24, 2006 at 05:29:59PM +0200, Rafael J. Wysocki wrote:
> On Tuesday, 24 October 2006 16:44, David Chinner wrote:
> > On Mon, Oct 23, 2006 at 12:36:53PM +0200, Rafael J. Wysocki wrote:
> > > On Monday, 23 October 2006 06:12, Nigel Cunningham wrote:
> > > > XFS can continue to submit I/O from a timer routine, even after
> > > > freezeable kernel and userspace threads are frozen. This doesn't seem to
> > > > be an issue for current swsusp code,
> > > 
> > > So it doesn't look like we need the patch _now_.
> > > 
> > > > but is definitely an issue for Suspend2, where the pages being written could
> > > > be overwritten by Suspend2's atomic copy.
> > > 
> > > And IMO that's a good reason why we shouldn't use RCU pages for storing the
> > > image.  XFS is one known example that breaks things if we do so and
> > > there may be more such things that we don't know of.  The fact that they
> > > haven't appeared in testing so far doesn't mean they don't exist and
> > > moreover some things like that may appear in the future.
> > 
> > Could you please tell us which XFS bits are broken so we can get
> > them fixed?  The XFS daemons should all be checking if they are
> > supposed to freeze (i.e. they call try_to_freeze() after they wake
> > up due to timer expiry) so I thought they were doing the right
> > thing.
> > 
> > However, I have to say that I agree with freezing the filesystems
> > before suspend - at least XFS will be in a consistent state that can
> > be recovered from without corruption if your machine fails to
> > resume....
> 
> Do you mean calling sys_sync() after the userspace has been frozen
> may not be sufficient?

In most cases it probably is, but sys_sync() doesn't provide any
guarantees that the filesystem is not being used or written to after
it completes. Given that every so often I hear about an XFS filesystem
that was corrupted by suspend, I don't think this is sufficient...

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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