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[80.230.31.118]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d7f66cd6bsm5144055e9.15.2026.01.05.12.35.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Jan 2026 12:35:41 -0800 (PST) Date: Mon, 5 Jan 2026 15:35:37 -0500 From: "Michael S. Tsirkin" To: Bui Quang Minh Cc: Jason Wang , netdev@vger.kernel.org, Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , 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 Subject: Re: [PATCH net v2 1/3] virtio-net: don't schedule delayed refill worker Message-ID: <20260105153517-mutt-send-email-mst@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> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: v-fqjUjhyfhbY0ylSS7SXhkyExyfYvltOACGvWxOHzA_1767645342 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Mon, Jan 05, 2026 at 10:03:22PM +0700, Bui Quang Minh wrote: > 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; >         } > >     } ok then, feel free to ignore this suggestion. > > > > > > > > > - > > > > > > > - 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.