Re: [PATCH] vfio/ccw: Remove WARN_ON during shutdown

Heiko Carstens
2023-02-12T18:09:47Z

On Fri, Feb 10, 2023 at 08:24:05PM -0500, Eric Farman wrote:
> On Fri, 2023-02-10 at 14:30 -0700, Alex Williamson wrote:
> > On Fri, 10 Feb 2023 18:42:27 +0100
> > Eric Farman <farman@linux.ibm.com> wrote:
> >
> > > The logic in vfio_ccw_sch_shutdown() always assumed that the input
> > > subchannel would point to a vfio_ccw_private struct, without
> > > checking
> > > that one exists. The blamed commit put in a check for this
> > > scenario,
> > > to prevent the possibility of a missing private.
> > >
> > > The trouble is that check was put alongside a WARN_ON(), presuming
> > > that such a scenario would be a cause for concern. But this can be
> > > triggered by binding a subchannel to vfio-ccw, and rebooting the
> > > system before starting the mdev (via "mdevctl start" or similar)
> > > or after stopping it. In those cases, shutdown doesn't need to
> > > worry because either the private was never allocated, or it was
> > > cleaned up by vfio_ccw_mdev_remove().
> > >
> > > Remove the WARN_ON() piece of this check, since there are plausible
> > > scenarios where private would be NULL in this path.
> > >
> > > Fixes: 9e6f07cd1eaa ("vfio/ccw: create a parent struct")
> > > Signed-off-by: Eric Farman <farman@linux.ibm.com>
> > > ---
> > >  drivers/s390/cio/vfio_ccw_drv.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
...
> > I see I'm on the To: line here, is this intended to go through the
> > vfio
> > tree rather than s390?
>
> Either way. I put you as "to" as the blamed commit went via vfio, but I
> could ask Heiko or Vasili to take it if that's easier.

I picked it up, so it will go via s390. Thanks!