Re: [PATCH 0/6] power: wire-up filesystem freeze/thaw with suspend/resume

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2025-04-02 at 09:46 +0200, Christian Brauner wrote:
> On Tue, Apr 01, 2025 at 01:02:07PM -0400, James Bottomley wrote:
> > On Tue, 2025-04-01 at 02:32 +0200, Christian Brauner wrote:
> > > The whole shebang can also be found at:
> > > https://web.git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/log/?h=work.freeze
> > > 
> > > I know nothing about power or hibernation. I've tested it as best
> > > as I could. Works for me (TM).
> > 
> > I'm testing the latest you have in work.freeze and it doesn't
> > currently work for me.  Patch 7b315c39b67d ("power: freeze
> > filesystems during suspend/resume") doesn't set
> > filesystems_freeze_ptr so it ends up being NULL and tripping over
> > this check 
> 
> I haven't pushed the new version there. Sorry about that. I only have
> it locally.
> 
> > 
> > +static inline bool may_unfreeze(struct super_block *sb, enum
> > freeze_holder who,
> > +                               const void *freeze_owner)
> > +{
> > +       WARN_ON_ONCE((who & ~FREEZE_FLAGS));
> > +       WARN_ON_ONCE(hweight32(who & FREEZE_HOLDERS) > 1);
> > +
> > +       if (who & FREEZE_EXCL) {
> > +               if (WARN_ON_ONCE(sb->s_writers.freeze_owner ==
> > NULL))
> > +                       return false;
> > 
> > 
> > in f15a9ae05a71 ("fs: add owner of freeze/thaw") and failing to
> > resume from hibernate.  Setting it to __builtin_return_address(0)
> > in filesystems_freeze() makes everything work as expected, so
> > that's what I'm testing now.
> 
> +1
> 
> I'll send the final version out in a bit.

I've now done some extensive testing on loop nested filesystems with
fio load on the upper. I've tried xfs on ext4 and ext4 on ext4.
Hibernate/Resume has currently worked on these without a hitch (and the
fio load burps a bit but then starts running at full speed within a few
seconds). What I'm doing is a single round of hibernate/resume followed
by a reboot. I'm relying on the fschecks to detect any filesystem
corruption. I've also tried doing a couple of fresh starts of the
hibernated image to check that we did correctly freeze the filesystems.

The problems I've noticed are:

   1. I'm using 9p to push host directories throught and that
      completely hangs after a resume. This is expected because the
      virtio server is out of sync, but it does indicate a need to
      address Jeff's question of what we should be doing for network
      filesystems (and is also the reason I have to reboot after
      resuming).
   2. Top doesn't show any CPU activity after resume even though fio is
      definitely running.  This seems to be a suspend issue and
      unrelated to filesystems, but I'll continue investigating.

Regards,

James