Re: [PATCH V6 9/9] virtio: use WARN_ON() to warning illegal status value

Michael S. Tsirkin
2022-05-27T10:50:11Z

At a minimum, I don't see why it's part of the series. Host can always
crash the guest if it wants to ...
The point of BUG_ON is device or driver is already corrupted so we
should not try to drive it. If you still want this in pls come up with
a better commit log explaining the why.

On Fri, May 27, 2022 at 02:01:20PM +0800, Jason Wang wrote:
> We used to use BUG_ON() in virtio_device_ready() to detect illegal

not really, BUG_ON just crashes the kernel. we detect by checking
status.

> status value, this seems sub-optimal since the value is under the
> control of the device. Switch to use WARN_ON() instead.

some people use crash on warn so ...

>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Halil Pasic <pasic@linux.ibm.com>
> Cc: Cornelia Huck <cohuck@redhat.com>
> Cc: Vineeth Vijayan <vneethv@linux.ibm.com>
> Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
> Cc: linux-s390@vger.kernel.org
> Signed-off-by: Jason Wang <jasowang@redhat.com>

> ---
> include/linux/virtio_config.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index d4edfd7d91bb..9a36051ceb76 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -255,7 +255,7 @@ void virtio_device_ready(struct virtio_device *dev)
> {
> unsigned status = dev->config->get_status(dev);
>
> - BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
> + WARN_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
>

we lose debuggability as guest will try to continue.
if we are doing this let us print a helpful message and dump a lot of
state right here.

> /*
> * The virtio_synchronize_cbs() makes sure vring_interrupt()
> --
> 2.25.1