Linux Virtualization - May 2022 - [PATCH V6 9/9] virtio: use WARN_ON() to warning illegal status value

We used to use BUG_ON() in virtio_device_ready() to detect illegal
status value, this seems sub-optimal since the value is under the
control of the device. Switch to use WARN_ON() instead.

Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: "Paul E. McKenney" <paulmck at kernel.org>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Halil Pasic <pasic at linux.ibm.com>
Cc: Cornelia Huck <cohuck at redhat.com>
Cc: Vineeth Vijayan <vneethv at linux.ibm.com>
Cc: Peter Oberparleiter <oberpar at linux.ibm.com>
Cc: linux-s390 at vger.kernel.org
Signed-off-by: Jason Wang <jasowang at 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);
 
 	/*
 	 * The virtio_synchronize_cbs() makes sure vring_interrupt()
-- 
2.25.1

On Fri, 27 May 2022 14:01:20 +0800, Jason Wang <jasowang at redhat.com>
wrote:
> We used to use BUG_ON() in virtio_device_ready() to detect illegal
> status value, this seems sub-optimal since the value is under the
> control of the device. Switch to use WARN_ON() instead.
>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: "Paul E. McKenney" <paulmck at kernel.org>
> Cc: Marc Zyngier <maz at kernel.org>
> Cc: Halil Pasic <pasic at linux.ibm.com>
> Cc: Cornelia Huck <cohuck at redhat.com>
> Cc: Vineeth Vijayan <vneethv at linux.ibm.com>
> Cc: Peter Oberparleiter <oberpar at linux.ibm.com>
> Cc: linux-s390 at vger.kernel.org
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo at linux.alibaba.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);
>
>  	/*
>  	 * The virtio_synchronize_cbs() makes sure vring_interrupt()
> --
> 2.25.1
>

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
>status value, this seems sub-optimal since the value is under the
>control of the device. Switch to use WARN_ON() instead.
>
>Cc: Thomas Gleixner <tglx at linutronix.de>
>Cc: Peter Zijlstra <peterz at infradead.org>
>Cc: "Paul E. McKenney" <paulmck at kernel.org>
>Cc: Marc Zyngier <maz at kernel.org>
>Cc: Halil Pasic <pasic at linux.ibm.com>
>Cc: Cornelia Huck <cohuck at redhat.com>
>Cc: Vineeth Vijayan <vneethv at linux.ibm.com>
>Cc: Peter Oberparleiter <oberpar at linux.ibm.com>
>Cc: linux-s390 at vger.kernel.org
>Signed-off-by: Jason Wang <jasowang at redhat.com>
>---
> include/linux/virtio_config.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Reviewed-by: Stefano Garzarella <sgarzare at redhat.com>

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