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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