On Fri, Nov 28, 2025 at 1:47 AM Bui Quang Minh <[email protected]> wrote:
>
> I think the the requeue in refill_work is not the problem here. In
> virtnet_rx_pause[_all](), we use cancel_work_sync() which is safe to
> use "even if the work re-queues itself". AFAICS, cancel_work_sync()
> will disable work -> flush work -> enable again. So if the work requeue
> itself in flush work, the requeue will fail because the work is already
> disabled.
Right.
>
> I think what triggers the deadlock here is a bug in
> virtnet_rx_resume_all(). virtnet_rx_resume_all() calls to
> __virtnet_rx_resume() which calls napi_enable() and may schedule
> refill. It schedules the refill work right after napi_enable the first
> receive queue. The correct way must be napi_enable all receive queues
> before scheduling refill work.
So what you meant is that the napi_disable() is called for a queue
whose NAPI has been disabled?
cpu0] enable_delayed_refill()
cpu0] napi_enable(queue0)
cpu0] schedule_delayed_work(&vi->refill)
cpu1] napi_disable(queue0)
cpu1] napi_enable(queue0)
cpu1] napi_disable(queue1)
In this case cpu1 waits forever while holding the netdev lock. This
looks like a bug since the netdev_lock 413f0271f3966 ("net: protect
NAPI enablement with netdev_lock()")?
>
> The fix is like this (there are quite duplicated code, I will clean up
> and send patches later if it is correct)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8e04adb57f52..892aa0805d1b 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3482,20 +3482,25 @@ static void __virtnet_rx_resume(struct virtnet_info
> *vi,
> static void virtnet_rx_resume_all(struct virtnet_info *vi)
> {
> int i;
> + bool schedule_refill = false;
> +
> + for (i = 0; i < vi->max_queue_pairs; i++)
> + __virtnet_rx_resume(vi, &vi->rq[i], false);
>
> enable_delayed_refill(vi);
> - for (i = 0; i < vi->max_queue_pairs; i++) {
> - if (i < vi->curr_queue_pairs)
> - __virtnet_rx_resume(vi, &vi->rq[i], true);
> - else
> - __virtnet_rx_resume(vi, &vi->rq[i], false);
> - }
> +
> + for (i = 0; i < vi->curr_queue_pairs; i++)
> + if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> + schedule_refill = true;
> +
> + if (schedule_refill)
> + schedule_delayed_work(&vi->refill, 0);
> }
>
> static void virtnet_rx_resume(struct virtnet_info *vi, struct receive_queue
> *rq)
> {
> - enable_delayed_refill(vi);
> __virtnet_rx_resume(vi, rq, true);
> + enable_delayed_refill(vi);
This seems to be odd. I think at least we need to move this before:
> + if (schedule_refill)
> + schedule_delayed_work(&vi->refill, 0);
?
> }
>
> static int virtnet_rx_resize(struct virtnet_info *vi,
>
> I also move the enable_delayed_refill() after we __virtnet_rx_resume()
> to ensure no refill is scheduled before napi_enable().
>
> What do you think?
This has been implemented in your patch or I may miss something.
Thanks
>
> Thanks,
> Quang Minh
>
