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Tsirkin" Cc: Jason Wang , netdev@vger.kernel.org, Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, stable@vger.kernel.org References: <20260102152023.10773-1-minhquangbui99@gmail.com> <20260102152023.10773-2-minhquangbui99@gmail.com> <6bac1895-d4a3-4e98-8f39-358fa14102db@gmail.com> <20260104085846-mutt-send-email-mst@kernel.org> <20260104100912-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Bui Quang Minh In-Reply-To: <20260104100912-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 1/4/26 22:12, Michael S. Tsirkin wrote: > On Sun, Jan 04, 2026 at 09:54:30PM +0700, Bui Quang Minh wrote: >> On 1/4/26 21:03, Michael S. Tsirkin wrote: >>> On Sun, Jan 04, 2026 at 03:34:52PM +0700, Bui Quang Minh wrote: >>>> On 1/4/26 13:09, Jason Wang wrote: >>>>> On Fri, Jan 2, 2026 at 11:20 PM 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 >>>>>> 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 >>>>>> Signed-off-by: Bui Quang Minh >>>>>> --- >>>>>> 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. >>>> That makes sense, I'll change it. >>>> >>>>>> 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. >>>> With GFP_KERNEL here, I think it's more likely to succeed than GFP_ATOMIC in >>>> NAPI poll. Another small benefit is that the actual packet can happen >>>> earlier. In case the receive buffer is empty and we don't refill here, the >>>> #1 NAPI poll refill the buffer and the #2 NAPI poll can receive packets. The >>>> #2 NAPI poll is scheduled in the interrupt handler because the #1 NAPI poll >>>> will deschedule the NAPI and enable the device interrupt. In case we >>>> successfully refill here, the #1 NAPI poll can receive packets right away. >>>> >>> Right. But I think this is a part that needs elucidating, not >>> error handling. >>> >>> /* Pre-fill rq agressively, to make sure we are ready to get packets >>> * immediately. >>> * */ >>> >>>>>> 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); >>> here the part that isn't clear is why are we refilling if !running >>> and what handles failures in that case. >> You are right, we should not refill when !running. I'll move the if (refill) >> inside the if (running). > Sounds like a helper that does refill+virtnet_napi_enable > would be in order then? fill_recv_aggressively(vi, rq) ? I think the helper can make the code a little more complicated. In virtnet_open(), the RX NAPI is enabled in virtnet_enable_queue_pair() so we need to add a flag like enable_rx. Then change the virtnet_open() to     for (i = 0; i < vi->max_queue_pairs; i++) {         if (i < vi->curr_queue_pairs) {             fill_recv_aggressively(vi, rq);             err = virtnet_enable_queue_pair(..., enable_rx = false);             if (err < 0)                 goto err_enable_qp;         } else {             err = virtnet_enable_queue_pair(..., enable_rx = true);             if (err < 0)                 goto err_enable_qp;         }     } > >>>>>> - >>>>>> - 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 >>>>> >>>> Thanks, >>>> Quang Minh.