Re: [PATCH] drm/virtio: add timeout to virtqueue wait to avoid hung task

[Ryosuke Yasuoka]

Thank you for the suggestions.

On 19/05/2026 09:11, Dmitry Osipenko wrote:
> On 5/18/26 09:45, Ryosuke Yasuoka wrote:
>>> It may be acceptable to have wait_event_timeout() in a loop, printing
>>> warnings about unresponsive host.
>> I considered this approach, but it does not solve the recovery problem
>> described above. The guest would still be stuck in the loop with no way
>> to remove the device or shut down gracefully.
> 
> Could `system_state != SYSTEM_RUNNING` be checked in the wait loop? This
> may allow to handle system shutdown, aborting the timed out wait in the
> special case.

Instead of checking system_state directly, I'm planning to add a driver
flag (e.g. vqs_released) to struct virtio_gpu_device. The shutdown path
(virtio_gpu_shutdown) will set this flag and wake up the wait queues
before calling drm_dev_unplug(). The wait loop checks the flag and
aborts if set. This may cover both the shutdown and the unbind cases
with a sinble check, so I believe a separate system_state check is not
needed. If my plan turns out to have issues, I will use system_state
check.

> Userspace may also get stuck in a zombie state. For that, code should
> use wait_event_interruptible(). But driver has code unprepared to be
> interrupted, it all needs to be reworked first [1].

Agreed. I will leave wait_event_interruptible() for follow-up once the
interruptible is prepared. For now, userspace stuck in D state remains a
pre-exsiting limitation.

> Similarly, for unbind there could a driver flag that the wait loop will
> check and handle specially.

Yes, the driver flag described above will handle this as well.

Best regards,
Ryosuke

> WDYT?
> 
> [1]
> https://lore.kernel.org/dri-devel/20260515084030.21986-1-kartikey406@xxxxxxxxx/