Re: [PATCH AUTOSEL 4.19 34/38] btrfs: file: reserve qgroup space after the hole punch range is locked

[Sasha Levin]

On Sat, Aug 29, 2020 at 02:11:23PM +0200, Pavel Machek wrote:
> Hi!
>
> > [ Upstream commit a7f8b1c2ac21bf081b41264c9cfd6260dffa6246 ]
> >
> > The incoming qgroup reserved space timing will move the data reservation
> > to ordered extent completely.
> >
> > However in btrfs_punch_hole_lock_range() will call
> > btrfs_invalidate_page(), which will clear QGROUP_RESERVED bit for the
> > range.
> >
> > In current stage it's OK, but if we're making ordered extents handle the
> > reserved space, then btrfs_punch_hole_lock_range() can clear the
> > QGROUP_RESERVED bit before we submit ordered extent, leading to qgroup
> > reserved space leakage.
> >
> > So here change the timing to make reserve data space after
> > btrfs_punch_hole_lock_range().
> > The new timing is fine for either current code or the new code.
>
> I'm not sure why this is queued for -stable. It is preparation for
> future work, and that work is not queued for -stable.

So you understand why it was queued: it's preparation for a fix that is
relevant to 4.19 but didn't apply cleanly.

I can look into what happened next week, or if you'd sent me a backport
I'd be happy to take it.

--
Thanks,
Sasha