Am Di., 16. Juni 2020 um 18:26 Uhr schrieb Darrick J. Wong
<darrick.wong@xxxxxxxxxx>:
> On Tue, Jun 16, 2020 at 03:57:08PM +0200, Andreas Gruenbacher wrote:
> > On Tue, Jun 16, 2020 at 3:23 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> > > On Tue, Jun 16, 2020 at 08:17:28AM -0400, Bob Peterson wrote:
> > > > ----- Original Message -----
> > > > > > I'd assume Andreas is looking at converting a filesystem to use iomap,
> > > > > > since this problem only occurs for filesystems which have returned an
> > > > > > invalid extent.
> > > > >
> > > > > Well, I can assume it's gfs2, but you know what happens when you
> > > > > assume something....
> > > >
> > > > Yes, it's gfs2, which already has iomap. I found the bug while just browsing
> > > > the code: gfs2 takes a lock in the begin code. If there's an error,
> > > > however unlikely, the end code is never called, so we would never unlock.
> > > > It doesn't matter to me whether the error is -EIO because it's very unlikely
> > > > in the first place. I haven't looked back to see where the problem was
> > > > introduced, but I suspect it should be ported back to stable releases.
> > >
> > > It shouldn't just be "unlikely", it should be impossible. This is the
> > > iomap code checking whether you've returned an extent which doesn't cover
> > > the range asked for. I don't think it needs to be backported, and I'm
> > > pretty neutral on whether it needs to be applied.
> >
> > Right, when these warnings trigger, the filesystem has already screwed
> > up; this fix only makes things less bad. Those kinds of issues are
> > very likely to be fixed long before the code hits users, so it
> > shouldn't be backported.
> >
> > This bug was in iomap_apply right from the start, so:
> >
> > Fixes: ae259a9c8593 ("fs: introduce iomap infrastructure")
>
> So... you found this through code inspection, and not because you
> actually hit this on gfs2, or any of the other iomap users?
Bob did, yes. I've only hit those warnings in the very early stages of
gfs2 iomap development, long before that code was even posted for
review.
> I generally think this looks ok, but I want to know if I should be
> looking deeper. :)
It's really supposed to be a simple, straight forward fix only.
Thanks,
Andreas
