On Sat, Jan 03, 2026 at 11:57:43AM -0500, Michael S. Tsirkin wrote:
> On Fri, Jan 02, 2026 at 10:20:21PM +0700, Bui Quang Minh wrote:
> > When we fail to refill the receive buffers, we schedule a delayed worker
> > to retry later. However, this worker creates some concurrency issues
> > such as races and deadlocks. To simplify the logic and avoid further
> > problems, we will instead retry refilling in the next NAPI poll.
> >
> > 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]
> > Suggested-by: Xuan Zhuo <[email protected]>
> > Signed-off-by: Bui Quang Minh <[email protected]>
> > ---
> > drivers/net/virtio_net.c | 55 ++++++++++++++++++++++------------------
> > 1 file changed, 30 insertions(+), 25 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 1bb3aeca66c6..ac514c9383ae 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -3035,7 +3035,7 @@ static int virtnet_receive_packets(struct
> > virtnet_info *vi,
> > }
> >
> > static int virtnet_receive(struct receive_queue *rq, int budget,
> > - unsigned int *xdp_xmit)
> > + unsigned int *xdp_xmit, bool *retry_refill)
> > {
> > struct virtnet_info *vi = rq->vq->vdev->priv;
> > struct virtnet_rq_stats stats = {};
> > @@ -3047,12 +3047,8 @@ static int virtnet_receive(struct receive_queue *rq,
> > int budget,
> > packets = virtnet_receive_packets(vi, rq, budget, xdp_xmit,
> > &stats);
> >
> > if (rq->vq->num_free > min((unsigned int)budget,
> > virtqueue_get_vring_size(rq->vq)) / 2) {
> > - if (!try_fill_recv(vi, rq, GFP_ATOMIC)) {
> > - spin_lock(&vi->refill_lock);
> > - if (vi->refill_enabled)
> > - schedule_delayed_work(&vi->refill, 0);
> > - spin_unlock(&vi->refill_lock);
> > - }
> > + if (!try_fill_recv(vi, rq, GFP_ATOMIC))
> > + *retry_refill = true;
> > }
> >
> > u64_stats_set(&stats.packets, packets);
> > @@ -3129,18 +3125,18 @@ static int virtnet_poll(struct napi_struct *napi,
> > int budget)
> > struct send_queue *sq;
> > unsigned int received;
> > unsigned int xdp_xmit = 0;
> > - bool napi_complete;
> > + bool napi_complete, retry_refill = false;
> >
> > virtnet_poll_cleantx(rq, budget);
> >
> > - received = virtnet_receive(rq, budget, &xdp_xmit);
> > + received = virtnet_receive(rq, budget, &xdp_xmit, &retry_refill);
> > rq->packets_in_napi += received;
> >
> > if (xdp_xmit & VIRTIO_XDP_REDIR)
> > xdp_do_flush();
> >
> > /* Out of packets? */
> > - if (received < budget) {
> > + if (received < budget && !retry_refill) {
> > napi_complete = virtqueue_napi_complete(napi, rq->vq, received);
> > /* Intentionally not taking dim_lock here. This may result in a
> > * spurious net_dim call. But if that happens
> > virtnet_rx_dim_work
> > @@ -3160,7 +3156,7 @@ static int virtnet_poll(struct napi_struct *napi, int
> > budget)
> > virtnet_xdp_put_sq(vi, sq);
> > }
> >
> > - return received;
> > + return retry_refill ? budget : received;
> > }
> >
> > static void virtnet_disable_queue_pair(struct virtnet_info *vi, int
> > qp_index)
> > @@ -3230,9 +3226,11 @@ static int virtnet_open(struct net_device *dev)
> >
> > 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);
> > + /* If this fails, we will retry later in
> > + * NAPI poll, which is scheduled in the below
> > + * virtnet_enable_queue_pair
>
> hmm do we even need this, then?
Oh this one is GFP_KERNEL. So it makes it more likely the ring will
be filled.
> > + */
> > + try_fill_recv(vi, &vi->rq[i], GFP_KERNEL);
> >
> > err = virtnet_enable_queue_pair(vi, i);
> > if (err < 0)
> > @@ -3473,15 +3471,15 @@ static void __virtnet_rx_resume(struct virtnet_info
> > *vi,
> > bool refill)
> > {
> > bool running = netif_running(vi->dev);
> > - bool schedule_refill = false;
> >
> > - if (refill && !try_fill_recv(vi, rq, GFP_KERNEL))
> > - schedule_refill = true;
> > + if (refill)
> > + /* If this fails, we will retry later in NAPI poll, which is
> > + * scheduled in the below virtnet_napi_enable
> > + */
> > + try_fill_recv(vi, rq, GFP_KERNEL);
>
>
> hmm do we even need this, then?
>
> > +
> > if (running)
> > virtnet_napi_enable(rq);
> > -
> > - if (schedule_refill)
> > - schedule_delayed_work(&vi->refill, 0);
> > }
> >
> > static void virtnet_rx_resume_all(struct virtnet_info *vi)
> > @@ -3777,6 +3775,7 @@ static int virtnet_set_queues(struct virtnet_info
> > *vi, u16 queue_pairs)
> > struct virtio_net_rss_config_trailer old_rss_trailer;
> > struct net_device *dev = vi->dev;
> > struct scatterlist sg;
> > + int i;
> >
> > if (!vi->has_cvq || !virtio_has_feature(vi->vdev, VIRTIO_NET_F_MQ))
> > return 0;
> > @@ -3829,11 +3828,17 @@ static int virtnet_set_queues(struct virtnet_info
> > *vi, u16 queue_pairs)
> > }
> > succ:
> > vi->curr_queue_pairs = queue_pairs;
> > - /* virtnet_open() will refill when device is going to up. */
> > - spin_lock_bh(&vi->refill_lock);
> > - if (dev->flags & IFF_UP && vi->refill_enabled)
> > - schedule_delayed_work(&vi->refill, 0);
> > - spin_unlock_bh(&vi->refill_lock);
> > + if (dev->flags & IFF_UP) {
> > + /* Let the NAPI poll refill the receive buffer for us. We can't
> > + * safely call try_fill_recv() here because the NAPI might be
> > + * enabled already.
> > + */
>
> I'd drop this comment, it does not clarify much.
>
> > + local_bh_disable();
> > + for (i = 0; i < vi->curr_queue_pairs; i++)
> > + virtqueue_napi_schedule(&vi->rq[i].napi, vi->rq[i].vq);
> > +
> > + local_bh_enable();
> > + }
> >
> > return 0;
> > }
> > --
> > 2.43.0
