[PATCH v4 1/4] virtio-net: disable delayed refill when pausing rx

Bui Quang Minh
2025-04-17T07:29:27Z

When pausing rx (e.g. set up xdp, xsk pool, rx resize), we call
napi_disable() on the receive queue's napi. In delayed refill_work, it
also calls napi_disable() on the receive queue's napi. When
napi_disable() is called on an already disabled napi, it will sleep in
napi_disable_locked while still holding the netdev_lock. As a result,
later napi_enable gets stuck too as it cannot acquire the netdev_lock.
This leads to refill_work and the pause-then-resume tx are stuck
altogether.

This scenario can be reproducible by binding a XDP socket to virtio-net
interface without setting up the fill ring. As a result, try_fill_recv
will fail until the fill ring is set up and refill_work is scheduled.

This commit adds virtnet_rx_(pause/resume)_all helpers and fixes up the
virtnet_rx_resume to disable future and cancel all inflights delayed
refill_work before calling napi_disable() to pause the rx.

Fixes: 413f0271f396 ("net: protect NAPI enablement with netdev_lock()")
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
---
drivers/net/virtio_net.c | 69 +++++++++++++++++++++++++++++++++-------
1 file changed, 57 insertions(+), 12 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7e4617216a4b..848fab51dfa1 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3342,7 +3342,8 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
return NETDEV_TX_OK;
}

-static void virtnet_rx_pause(struct virtnet_info *vi, struct receive_queue *rq)
+static void __virtnet_rx_pause(struct virtnet_info *vi,
+ struct receive_queue *rq)
{
bool running = netif_running(vi->dev);

@@ -3352,17 +3353,63 @@ static void virtnet_rx_pause(struct virtnet_info *vi, struct receive_queue *rq)
}
}

-static void virtnet_rx_resume(struct virtnet_info *vi, struct receive_queue *rq)
+static void virtnet_rx_pause_all(struct virtnet_info *vi)
+{
+ int i;
+
+ /*
+ * Make sure refill_work does not run concurrently to
+ * avoid napi_disable race which leads to deadlock.
+ */
+ disable_delayed_refill(vi);
+ cancel_delayed_work_sync(&vi->refill);
+ for (i = 0; i < vi->max_queue_pairs; i++)
+ __virtnet_rx_pause(vi, &vi->rq[i]);
+}
+
+static void virtnet_rx_pause(struct virtnet_info *vi, struct receive_queue *rq)
+{
+ /*
+ * Make sure refill_work does not run concurrently to
+ * avoid napi_disable race which leads to deadlock.
+ */
+ disable_delayed_refill(vi);
+ cancel_delayed_work_sync(&vi->refill);
+ __virtnet_rx_pause(vi, rq);
+}
+
+static void __virtnet_rx_resume(struct virtnet_info *vi,
+ struct receive_queue *rq,
+ bool refill)
{
bool running = netif_running(vi->dev);

- if (!try_fill_recv(vi, rq, GFP_KERNEL))
+ if (refill && !try_fill_recv(vi, rq, GFP_KERNEL))
schedule_delayed_work(&vi->refill, 0);

if (running)
virtnet_napi_enable(rq);
}

+static void virtnet_rx_resume_all(struct virtnet_info *vi)
+{
+ int i;
+
+ enable_delayed_refill(vi);
+ for (i = 0; i < vi->max_queue_pairs; i++) {
+ if (i < vi->curr_queue_pairs)
+ __virtnet_rx_resume(vi, &vi->rq[i], true);
+ else
+ __virtnet_rx_resume(vi, &vi->rq[i], false);
+ }
+}
+
+static void virtnet_rx_resume(struct virtnet_info *vi, struct receive_queue *rq)
+{
+ enable_delayed_refill(vi);
+ __virtnet_rx_resume(vi, rq, true);
+}
+
static int virtnet_rx_resize(struct virtnet_info *vi,
struct receive_queue *rq, u32 ring_num)
{
@@ -5959,12 +6006,12 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
if (prog)
bpf_prog_add(prog, vi->max_queue_pairs - 1);

+ virtnet_rx_pause_all(vi);
+
/* Make sure NAPI is not using any XDP TX queues for RX. */
if (netif_running(dev)) {
- for (i = 0; i < vi->max_queue_pairs; i++) {
- virtnet_napi_disable(&vi->rq[i]);
+ for (i = 0; i < vi->max_queue_pairs; i++)
virtnet_napi_tx_disable(&vi->sq[i]);
- }
}

if (!prog) {
@@ -5996,13 +6043,12 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
vi->xdp_enabled = false;
}

+ virtnet_rx_resume_all(vi);
for (i = 0; i < vi->max_queue_pairs; i++) {
if (old_prog)
bpf_prog_put(old_prog);
- if (netif_running(dev)) {
- virtnet_napi_enable(&vi->rq[i]);
+ if (netif_running(dev))
virtnet_napi_tx_enable(&vi->sq[i]);
- }
}

return 0;
@@ -6014,11 +6060,10 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
rcu_assign_pointer(vi->rq[i].xdp_prog, old_prog);
}

+ virtnet_rx_resume_all(vi);
if (netif_running(dev)) {
- for (i = 0; i < vi->max_queue_pairs; i++) {
- virtnet_napi_enable(&vi->rq[i]);
+ for (i = 0; i < vi->max_queue_pairs; i++)
virtnet_napi_tx_enable(&vi->sq[i]);
- }
}
if (prog)
bpf_prog_sub(prog, vi->max_queue_pairs - 1);
--
2.43.0