Re: [PATCH net v3 1/3] virtio-net: don't schedule delayed refill worker
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2026-01-06 15:29:15
Also in:
bpf, lkml, stable, virtualization
On Tue, Jan 06, 2026 at 10:04:36PM +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.
For example, when the worker runs concurrently with virtnet_xdp_set,
both need to temporarily disable queue's NAPI before enabling again.
Without proper synchronization, a deadlock can happen when
napi_disable() is called on an already disabled NAPI. That
napi_disable() call will be stuck and so will the subsequent
napi_enable() call.
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 <redacted>Acked-by: Michael S. Tsirkin <mst@redhat.com> and CC stable I think. Can you do that pls?
quoted hunk ↗ jump to hunk
--- drivers/net/virtio_net.c | 48 +++++++++++++++++++++------------------- 1 file changed, 25 insertions(+), 23 deletions(-)diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 1bb3aeca66c6..f986abf0c236 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c@@ -3046,16 +3046,16 @@ static int virtnet_receive(struct receive_queue *rq, int budget, else packets = virtnet_receive_packets(vi, rq, budget, xdp_xmit, &stats); + u64_stats_set(&stats.packets, packets); 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)) + /* We need to retry refilling in the next NAPI poll so + * we must return budget to make sure the NAPI is + * repolled. + */ + packets = budget; } - u64_stats_set(&stats.packets, packets); u64_stats_update_begin(&rq->stats.syncp); for (i = 0; i < ARRAY_SIZE(virtnet_rq_stats_desc); i++) { size_t offset = virtnet_rq_stats_desc[i].offset;@@ -3230,9 +3230,10 @@ 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); + /* Pre-fill rq agressively, to make sure we are ready to + * get packets immediately. + */ + try_fill_recv(vi, &vi->rq[i], GFP_KERNEL); err = virtnet_enable_queue_pair(vi, i); if (err < 0)@@ -3472,16 +3473,15 @@ static void __virtnet_rx_resume(struct virtnet_info *vi, struct receive_queue *rq, bool refill) { - bool running = netif_running(vi->dev); - bool schedule_refill = false; + if (netif_running(vi->dev)) { + /* Pre-fill rq agressively, to make sure we are ready to get + * packets immediately. + */ + if (refill) + try_fill_recv(vi, rq, GFP_KERNEL); - if (refill && !try_fill_recv(vi, rq, GFP_KERNEL)) - schedule_refill = true; - 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)@@ -3829,11 +3829,13 @@ 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) { + local_bh_disable(); + for (int 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