linux-kernel - Re: [RFC][PATCH] PM / Freezer: Freeze filesystems along with freezing processes (was: Re: PM / hibernate xfs lock up / xfs_reclaim_inodes

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Date:	Wed, 3 Aug 2011 19:29:22 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Nigel Cunningham <nigel@...onice.net>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	Christoph <cr2005@...lub.de>,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	xfs@....sgi.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM / Freezer: Freeze filesystems along with
 freezing processes (was: Re: PM / hibernate xfs lock up /
 xfs_reclaim_inodes_ag)

Hi!

> Freeze all filesystems during the freezing of tasks by calling
> freeze_bdev() for each of them and thaw them during the thawing
> of tasks with the help of thaw_bdev().
> 
> This is needed by hibernation, because some filesystems (e.g. XFS)
> deadlock with the preallocation of memory used by it if the memory
> pressure caused by it is too heavy.
> 
> The additional benefit of this change is that, if something goes
> wrong after filesystems have been frozen, they will stay in a
> consistent state and journal replays won't be necessary (e.g. after
> a failing suspend or resume).  In particular, this should help to
> solve a long-standing issue that in some cases during resume from
> hibernation the boot loader causes the journal to be replied for the
> filesystem containing the kernel image and initrd causing it to
> become inconsistent with the information stored in the hibernation
> image.

> +/**
> + * freeze_filesystems - Force all filesystems into a consistent state.
> + */
> +void freeze_filesystems(void)
> +{
> +	struct super_block *sb;
> +
> +	lockdep_off();

Ouch. So... why do we need to silence this?

> +	/*
> +	 * Freeze in reverse order so filesystems dependant upon others are
> +	 * frozen in the right order (eg. loopback on ext3).
> +	 */
> +	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
> +		if (!sb->s_root || !sb->s_bdev ||
> +		    (sb->s_frozen == SB_FREEZE_TRANS) ||
> +		    (sb->s_flags & MS_RDONLY) ||
> +		    (sb->s_flags & MS_FROZEN))
> +			continue;

Should we stop NFS from modifying remote server, too?

Plus... ext3 writes to read-only filesystems on mount; not sure if it
does it later. But RDONLY means 'user cant write to it' not 'bdev will
not be modified'. Should we freeze all?

How can 'already frozen' happen?

> +	list_for_each_entry(sb, &super_blocks, s_list)
> +		if (sb->s_flags & MS_FROZEN) {
> +			sb->s_flags &= ~MS_FROZEN;
> +			thaw_bdev(sb->s_bdev, sb);
> +		}

...because we'll unfreeze it even if we did not freeze it...

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