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

["Denis V. Lunev" <den@virtuozzo.com>]

On 6/24/26 16:55, David Hildenbrand (Arm) wrote:
> 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>
>
I would spend more time with other drivers once we will
done with this. I have strong candidate - virtio-mem.

Den