Re: [PATCH v2] iomap: Make sure iomap_end is called after iomap_begin

[Christoph Hellwig <hch@infradead.org>]

On Mon, Jun 22, 2020 at 11:07:59AM +0200, Andreas Gruenbacher wrote:
> On Fri, Jun 19, 2020 at 3:25 PM Christoph Hellwig <hch@infradead.org> wrote:
> > On Thu, Jun 18, 2020 at 02:24:08PM +0200, Andreas Gruenbacher wrote:
> > > Make sure iomap_end is always called when iomap_begin succeeds.
> > >
> > > Without this fix, iomap_end won't be called when a filesystem's
> > > iomap_begin operation returns an invalid mapping, bypassing any
> > > unlocking done in iomap_end.  With this fix, the unlocking would
> > > at least still happen.
> > >
> > > This iomap_apply bug was found by Bob Peterson during code review.
> > > It's unlikely that such iomap_begin bugs will survive to affect
> > > users, so backporting this fix seems unnecessary.
> > >
> > > Fixes: ae259a9c8593 ("fs: introduce iomap infrastructure")
> > > Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> > > ---
> > >  fs/iomap/apply.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c
> > > index 76925b40b5fd..32daf8cb411c 100644
> > > --- a/fs/iomap/apply.c
> > > +++ b/fs/iomap/apply.c
> > > @@ -46,10 +46,11 @@ iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags,
> > >       ret = ops->iomap_begin(inode, pos, length, flags, &iomap, &srcmap);
> > >       if (ret)
> > >               return ret;
> > > -     if (WARN_ON(iomap.offset > pos))
> > > -             return -EIO;
> > > -     if (WARN_ON(iomap.length == 0))
> > > -             return -EIO;
> > > +     if (WARN_ON(iomap.offset > pos) ||
> > > +         WARN_ON(iomap.length == 0)) {
> > > +             written = -EIO;
> > > +             goto out;
> > > +     }
> >
> > As said before please don't merge these for no good reason.
> 
> I really didn't expect this tiny patch to require much discussion at
> all, but just to be clear ... do you actually object to this very
> patch that explicitly doesn't merge the two checks and keeps them on
> two separate lines so that the warning messages will report different
> line numbers, or are you fine with that?

Yes, it merges the WARN_ONs, and thus reduces their usefulness.  How
about a patch that just fixes your reported issue insted of messing up
other things for no good reason?