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Message-ID: <54e15e32-ee0d-4677-a85d-eb54ffe60a77@gmail.com>
Date: Sun, 4 Jan 2026 11:33:20 +0700
From: Bui Quang Minh <minhquangbui99@...il.com>
To: "Michael S. Tsirkin" <mst@...hat.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 1/3/26 23:57, 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 <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.
Here I want to note on why we can't use try_fill_recv like in other places.
>
>> + 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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