Re: [PATCH net v2 1/3] virtio-net: don't schedule delayed refill worker

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Jan 04, 2026 at 02:09:06PM +0800, Jason Wang wrote:
> On Fri, Jan 2, 2026 at 11:20 PM Bui Quang Minh <minhquangbui99@gmail.com> 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 <pabeni@redhat.com>
> > Closes: https://netdev-ctrl.bots.linux.dev/logs/vmksft/drv-hw-dbg/results/400961/3-xdp-py/stderr
> > Cc: stable@vger.kernel.org
> > Suggested-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
> > ---
> >  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);
> 
> I think we can simply let virtnet_receive() to return the budget when
> reill fails.

Great idea.

> >         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
> > +                        */
> > +                       try_fill_recv(vi, &vi->rq[i], GFP_KERNEL);
> 
> Consider NAPI will be eventually scheduled, I wonder if it's still
> worth to refill here.
> 
> >
> >                 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);
> 
> and here.
> 
> > +
> >         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.
> > +                */
> > +               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
> >
> 
> Thanks