Re: [RFC][PATCH] PM / Freezer: Freeze filesystems along with freezing processes (was: Re: PM / hibernate xfs lock up / xfs_reclaim_inodes_ag)

Rafael J. Wysocki
2011-08-04T09:26:25Z

On Wednesday, August 03, 2011, Pavel Machek wrote:
> 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?

So that it doesn't complain? :-)

I'll need some time to get the exact details here.

> > + /*
> > + * 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?

What do you mean exactly?

> 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...

So we need not check MS_FROZEN in freeze_filesystems(). OK

Thanks,