On Fri, Dec 12, 2025 at 11:28 PM Bui Quang Minh
<[email protected]> wrote:
>
> Calling napi_disable() on an already disabled napi can cause the
> deadlock. In commit 4bc12818b363 ("virtio-net: disable delayed refill
> when pausing rx"), to avoid the deadlock, when pausing the RX in
> virtnet_rx_pause[_all](), we disable and cancel the delayed refill work.
> However, in the virtnet_rx_resume_all(), we enable the delayed refill
> work too early before enabling all the receive queue napis.
>
> The deadlock can be reproduced by running
> selftests/drivers/net/hw/xsk_reconfig.py with multiqueue virtio-net
> device and inserting a cond_resched() inside the for loop in
> virtnet_rx_resume_all() to increase the success rate. Because the worker
> processing the delayed refilled work runs on the same CPU as
> virtnet_rx_resume_all(), a reschedule is needed to cause the deadlock.
> In real scenario, the contention on netdev_lock can cause the
> reschedule.
>
> This fixes the deadlock by ensuring all receive queue's napis are
> enabled before we enable the delayed refill work in
> virtnet_rx_resume_all() and virtnet_open().
>
> Fixes: 4bc12818b363 ("virtio-net: disable delayed refill when pausing rx")
> Reported-by: Paolo Abeni <[email protected]>
> Closes:
> https://netdev-ctrl.bots.linux.dev/logs/vmksft/drv-hw-dbg/results/400961/3-xdp-py/stderr
> Cc: [email protected]
> Signed-off-by: Bui Quang Minh <[email protected]>
> ---
> Changes in v2:
> - Move try_fill_recv() before rx napi_enable()
> - Link to v1:
> https://lore.kernel.org/netdev/[email protected]/
> ---
> drivers/net/virtio_net.c | 71 +++++++++++++++++++++++++---------------
> 1 file changed, 45 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8e04adb57f52..4e08880a9467 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3214,21 +3214,31 @@ static void virtnet_update_settings(struct
> virtnet_info *vi)
> static int virtnet_open(struct net_device *dev)
> {
> struct virtnet_info *vi = netdev_priv(dev);
> + bool schedule_refill = false;
> int i, err;
>
> - enable_delayed_refill(vi);
> -
> + /* - We must call try_fill_recv before enabling napi of the same
> receive
> + * queue so that it doesn't race with the call in virtnet_receive.
> + * - We must enable and schedule delayed refill work only when we have
> + * enabled all the receive queue's napi. Otherwise, in refill_work, we
> + * have a deadlock when calling napi_disable on an already disabled
> + * napi.
> + */
> for (i = 0; i < vi->max_queue_pairs; i++) {
> if (i < vi->curr_queue_pairs)
> /* Make sure we have some buffers: if oom use wq. */
> if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> - schedule_delayed_work(&vi->refill, 0);
> + schedule_refill = true;
>
> err = virtnet_enable_queue_pair(vi, i);
> if (err < 0)
> goto err_enable_qp;
> }
So NAPI could be scheduled and it may want to refill but since refill
is not enabled, there would be no refill work.
Is this a problem?
>
> + enable_delayed_refill(vi);
> + if (schedule_refill)
> + schedule_delayed_work(&vi->refill, 0);
> +
> if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
> if (vi->status & VIRTIO_NET_S_LINK_UP)
> netif_carrier_on(vi->dev);
> @@ -3463,39 +3473,48 @@ static void virtnet_rx_pause(struct virtnet_info *vi,
> struct receive_queue *rq)
> __virtnet_rx_pause(vi, rq);
> }
>
Thanks
