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

[Christian Brauner]

On Tue, Apr 08, 2025 at 11:43:46AM -0400, James Bottomley wrote:
> 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).

No network filesystem supports freeze/thaw so they're not frozen/thawed
during hibernation.

virtiofs doesn't support filesystem freezing either and it warns about
virtio_driver based freezing not being implemented.