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

[Alex Williamson <alex.williamson@redhat.com>]

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(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
> index 54aba7cceb33..ff538a086fc7 100644
> --- a/drivers/s390/cio/vfio_ccw_drv.c
> +++ b/drivers/s390/cio/vfio_ccw_drv.c
> @@ -225,7 +225,7 @@ static void vfio_ccw_sch_shutdown(struct subchannel *sch)
>  	struct vfio_ccw_parent *parent = dev_get_drvdata(&sch->dev);
>  	struct vfio_ccw_private *private = dev_get_drvdata(&parent->dev);
>  
> -	if (WARN_ON(!private))
> +	if (!private)
>  		return;
>  
>  	vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_CLOSE);

I see I'm on the To: line here, is this intended to go through the vfio
tree rather than s390?  Thanks,

Alex