Re: [PATCH v2 3/4] virtio_balloon: quiesce balloon work before device shutdown

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/24/26 16:08, Denis V. Lunev wrote:
> Commit 8bd2fa086a04 ("virtio: break and reset virtio devices on
> device_shutdown()") added a generic virtio bus .shutdown handler that
> breaks and resets every virtio device during device_shutdown(), i.e. on
> reboot and kexec.
> 
> virtio_balloon provides no .shutdown of its own, so that generic path
> runs while the balloon's asynchronous work is still armed. Once the
> device has been broken, virtqueue_add_inbuf() in
> virtballoon_free_page_report() returns -EIO and trips its
> WARN_ON_ONCE(). On a kernel booted with panic_on_warn that turns an
> ordinary reboot, for example a kexec based upgrade, into a fatal panic
> in the middle of device_shutdown(), so the machine never reaches the
> new kernel.
> 
> Relaxing that single WARN_ON_ONCE() would only hide the symptom: the
> inflate/deflate and OOM paths do not warn, they call
> wait_event(vb->acked, ...) and would instead block forever on a broken
> queue that can no longer complete. The device has to be quiesced, not
> just kept quiet.
> 
> Add a .shutdown handler that quiesces the balloon via the shared
> virtballoon_quiesce() helper while the device is still alive, and only
> then breaks and resets it via virtio_device_shutdown(). Unlike
> virtballoon_remove() the balloon workqueue is not destroyed, as shutdown
> does not free the device and cancel_work_sync() together with stop_update
> already prevent any further work from being queued.
> 
> Fixes: 8bd2fa086a04 ("virtio: break and reset virtio devices on device_shutdown()")
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> ---
>  drivers/virtio/virtio_balloon.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 5b02d9191ac6..26fc3c40d5b2 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -1137,6 +1137,12 @@ static void virtballoon_remove(struct virtio_device *vdev)
>  	kfree(vb);
>  }
>  
> +static void virtballoon_shutdown(struct virtio_device *vdev)
> +{
> +	virtballoon_quiesce(vdev->priv);
> +	virtio_device_shutdown(vdev);
> +}

I'm curious why virtio_gpu_shutdown() doesn't need that (did not look into the
details).

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David