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Message-ID: <20260103115424-mutt-send-email-mst@kernel.org>
Date: Sat, 3 Jan 2026 11:57:37 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Bui Quang Minh <minhquangbui99@...il.com>
Cc: netdev@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
Eugenio Pérez <eperezma@...hat.com>,
Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
Stanislav Fomichev <sdf@...ichev.me>,
virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
bpf@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net v2 1/3] virtio-net: don't schedule delayed refill
worker
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 <pabeni@...hat.com>
> Closes: https://netdev-ctrl.bots.linux.dev/logs/vmksft/drv-hw-dbg/results/400961/3-xdp-py/stderr
> Cc: stable@...r.kernel.org
> Suggested-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.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);
> 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?
> + */
> + 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
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