Re: [LSF/MM/BPF TOPIC] Filesystem Suspend Resume

James Bottomley
2025-03-21T12:34:03Z

On Thu, 2025-03-20 at 22:23 -0700, Christoph Hellwig wrote:
> On Thu, Mar 20, 2025 at 02:15:15PM -0400, James Bottomley wrote:
> > On Thu, 2025-03-20 at 09:48 -0700, Christoph Hellwig wrote:
> > [...]
> > > We finally got hibernate to freeze file system on suspend,
> >
> > I was looking for this to see if I could possibly plug something in
> > for pseudo filesystems that don't have backing devices.  However, I
> > can't find the path where suspend causes freeze (at least the bdev
> > doesn't seem to register any power notifier like the scsi block
> > device does), where is the code?
>
> Looking again I can't find it either.  On the internet I find a patch
> adding it from 2006:
>
> https://groups.google.com/g/fa.linux.kernel/c/dtxsNJ7ks58/m/mqU8SIAbvLgJ

Wow google has a terrible interface. This is the lore link:

https://lore.kernel.org/all/200611011200.18438.rjw@sisk.pl/

So the patch indicates where to put direct hooks in the power
management but it operates via bdev_freeze/thaw() which wouldn't work
for pseudo filesystems, but could be replaced by a direct hook into the
vfs that would iterate over superblocks calling
freeze_super/thaw_super().

> But I couldn't see if it got applied or disappaeared again somehow.
> Adding the relevant maintainers.

It looks like it got reposted about 5 years later as well (in the
middle of a thread about xfs hibernate lockups):

https://lore.kernel.org/all/201108032315.06012.rjw__14254.1066081778$1312406161$gmane$org@sisk.pl/

Then again 6 months later:

https://lore.kernel.org/all/201201281445.49377.rjw@sisk.pl/

everything kept foundering on deadlock problems between filesystems
needing threads to shrink and complete writeout and the freezing of
those threads.

Let me digest all that and see if we have more hope this time around.

Regards,

James