Re: [PATCH] ceph: decoding error in ceph_update_snap_realm should return -EIO

[Ilya Dryomov <idryomov@gmail.com>]

On Thu, Jun 3, 2021 at 4:02 PM Jeff Layton <jlayton@kernel.org> wrote:
>
> On Thu, 2021-06-03 at 15:57 +0200, Ilya Dryomov wrote:
> > On Thu, Jun 3, 2021 at 3:39 PM Jeff Layton <jlayton@kernel.org> wrote:
> > >
> > > Currently ceph_update_snap_realm returns -EINVAL when it hits a decoding
> > > error, which is the wrong error code. -EINVAL implies that the user gave
> > > us a bogus argument to a syscall or something similar. -EIO is more
> > > descriptive when we hit a decoding error.
> > >
> > > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > > ---
> > >  fs/ceph/snap.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> > > index d07c1c6ac8fb..f8cac2abab3f 100644
> > > --- a/fs/ceph/snap.c
> > > +++ b/fs/ceph/snap.c
> > > @@ -807,7 +807,7 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
> > >         return 0;
> > >
> > >  bad:
> > > -       err = -EINVAL;
> > > +       err = -EIO;
> > >  fail:
> > >         if (realm && !IS_ERR(realm))
> > >                 ceph_put_snap_realm(mdsc, realm);
> >
> > Hi Jeff,
> >
> > Is this error code propagated anywhere important?
> >
> > The vast majority of functions that have something to do with decoding
> > use EINVAL as a default (usually out-of-bounds) error.  I agree that it
> > is totally ambiguous, but EIO doesn't seem to be any better to me.  If
> > there is a desire to separate these errors, I think we need to pick
> > something much more distinctive.
> >
>
> When I see EINVAL, I automatically wonder what bogus argument I passed
> in somewhere, so I find that particularly deceptive here where the bug
> is either from the MDS or we had some sort of low-level socket handling
> problem.
>
> OTOH, you have a good point. The callers universally ignore the error
> code from this function. Perhaps we ought to just log a pr_warn message
> or something if the decoding fails here instead?

There already is one:

 793 bad:
 794         err = -EINVAL;
 795 fail:
 796         if (realm && !IS_ERR(realm))
 797                 ceph_put_snap_realm(mdsc, realm);
 798         if (first_realm)
 799                 ceph_put_snap_realm(mdsc, first_realm);
 800         pr_err("update_snap_trace error %d\n", err);
 801         return err;

Or do you mean specifically the "bad" label?

Thanks,

                Ilya