[PATCH net v3 0/3] virtio-net: fix the deadlock when disabling rx NAPI

[PATCH net v3 0/3] virtio-net: fix the deadlock when disabling rx NAPI

[Bui Quang Minh]

Calling napi_disable() on an already disabled napi can cause the
deadlock. In commit 4bc12818b363 ("virtio-net: disable delayed refill
when pausing rx"), to avoid the deadlock, when pausing the RX in
virtnet_rx_pause[_all](), we disable and cancel the delayed refill work.
However, in the virtnet_rx_resume_all(), we enable the delayed refill
work too early before enabling all the receive queue napis.

The deadlock can be reproduced by running
selftests/drivers/net/hw/xsk_reconfig.py with multiqueue virtio-net
device and inserting a cond_resched() inside the for loop in
virtnet_rx_resume_all() to increase the success rate. Because the worker
processing the delayed refilled work runs on the same CPU as
virtnet_rx_resume_all(), a reschedule is needed to cause the deadlock.
In real scenario, the contention on netdev_lock can cause the
reschedule.

Due to the complexity of delayed refill worker, in this series, we remove
it. When we fail to refill the receive buffer, we will retry in the next
NAPI poll instead.
- Patch 1: removes delayed refill worker schedule and retry refill in next
NAPI
- Patch 2, 3: removes and clean up unused delayed refill worker code

For testing, I've run the following tests with no issue so far
- selftests/drivers/net/hw/xsk_reconfig.py which sets up the XDP zerocopy
without providing any descriptors to the fill ring. As a result,
try_fill_recv will always fail.
- Send TCP packets from host to guest while guest is nearly OOM and some
try_fill_recv calls fail.

Changes in v3:
- Patch 1: return budget when needing to retry in next NAPI in
virtnet_receive, fix comments and commit message
- Patch 2: edit the commit message
- Link to v2:
https://lore.kernel.org/netdev/20260102152023.10773-1-minhquangbui99@gmail.com/

Changes in v2:
- Remove the delayed refill worker to simplify the logic instead of trying
to fix it
- Link to v1:
https://lore.kernel.org/netdev/20251223152533.24364-1-minhquangbui99@gmail.com/

Link to the previous approach and discussion:
https://lore.kernel.org/netdev/20251212152741.11656-1-minhquangbui99@gmail.com/

Thanks,
Quang Minh.

Bui Quang Minh (3):
  virtio-net: don't schedule delayed refill worker
  virtio-net: remove unused delayed refill worker
  virtio-net: clean up __virtnet_rx_pause/resume

 drivers/net/virtio_net.c | 164 +++++++++------------------------------
 1 file changed, 35 insertions(+), 129 deletions(-)

-- 
2.43.0

[PATCH net v3 1/3] virtio-net: don't schedule delayed refill worker

[Bui Quang Minh]

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 <minhquangbui99@gmail.com>
---
 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

[PATCH net v3 2/3] virtio-net: remove unused delayed refill worker

[Bui Quang Minh]

Since we switched to retry refilling receive buffer in NAPI poll instead
of delayed worker, remove all now unused delayed refill worker code.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
---
 drivers/net/virtio_net.c | 86 ----------------------------------------
 1 file changed, 86 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index f986abf0c236..a4dbc958689b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -441,9 +441,6 @@ struct virtnet_info {
 	/* Packet virtio header size */
 	u8 hdr_len;
 
-	/* Work struct for delayed refilling if we run low on memory. */
-	struct delayed_work refill;
-
 	/* UDP tunnel support */
 	bool tx_tnl;
 
@@ -451,12 +448,6 @@ struct virtnet_info {
 
 	bool rx_tnl_csum;
 
-	/* Is delayed refill enabled? */
-	bool refill_enabled;
-
-	/* The lock to synchronize the access to refill_enabled */
-	spinlock_t refill_lock;
-
 	/* Work struct for config space updates */
 	struct work_struct config_work;
 
@@ -720,20 +711,6 @@ static void virtnet_rq_free_buf(struct virtnet_info *vi,
 		put_page(virt_to_head_page(buf));
 }
 
-static void enable_delayed_refill(struct virtnet_info *vi)
-{
-	spin_lock_bh(&vi->refill_lock);
-	vi->refill_enabled = true;
-	spin_unlock_bh(&vi->refill_lock);
-}
-
-static void disable_delayed_refill(struct virtnet_info *vi)
-{
-	spin_lock_bh(&vi->refill_lock);
-	vi->refill_enabled = false;
-	spin_unlock_bh(&vi->refill_lock);
-}
-
 static void enable_rx_mode_work(struct virtnet_info *vi)
 {
 	rtnl_lock();
@@ -2948,42 +2925,6 @@ static void virtnet_napi_disable(struct receive_queue *rq)
 	napi_disable(napi);
 }
 
-static void refill_work(struct work_struct *work)
-{
-	struct virtnet_info *vi =
-		container_of(work, struct virtnet_info, refill.work);
-	bool still_empty;
-	int i;
-
-	for (i = 0; i < vi->curr_queue_pairs; i++) {
-		struct receive_queue *rq = &vi->rq[i];
-
-		/*
-		 * When queue API support is added in the future and the call
-		 * below becomes napi_disable_locked, this driver will need to
-		 * be refactored.
-		 *
-		 * One possible solution would be to:
-		 *   - cancel refill_work with cancel_delayed_work (note:
-		 *     non-sync)
-		 *   - cancel refill_work with cancel_delayed_work_sync in
-		 *     virtnet_remove after the netdev is unregistered
-		 *   - wrap all of the work in a lock (perhaps the netdev
-		 *     instance lock)
-		 *   - check netif_running() and return early to avoid a race
-		 */
-		napi_disable(&rq->napi);
-		still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
-		virtnet_napi_do_enable(rq->vq, &rq->napi);
-
-		/* In theory, this can happen: if we don't get any buffers in
-		 * we will *never* try to fill again.
-		 */
-		if (still_empty)
-			schedule_delayed_work(&vi->refill, HZ/2);
-	}
-}
-
 static int virtnet_receive_xsk_bufs(struct virtnet_info *vi,
 				    struct receive_queue *rq,
 				    int budget,
@@ -3226,8 +3167,6 @@ static int virtnet_open(struct net_device *dev)
 	struct virtnet_info *vi = netdev_priv(dev);
 	int i, err;
 
-	enable_delayed_refill(vi);
-
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		if (i < vi->curr_queue_pairs)
 			/* Pre-fill rq agressively, to make sure we are ready to
@@ -3252,9 +3191,6 @@ static int virtnet_open(struct net_device *dev)
 	return 0;
 
 err_enable_qp:
-	disable_delayed_refill(vi);
-	cancel_delayed_work_sync(&vi->refill);
-
 	for (i--; i >= 0; i--) {
 		virtnet_disable_queue_pair(vi, i);
 		virtnet_cancel_dim(vi, &vi->rq[i].dim);
@@ -3448,24 +3384,12 @@ 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);
 }
 
@@ -3488,7 +3412,6 @@ 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);
@@ -3499,7 +3422,6 @@ static void virtnet_rx_resume_all(struct virtnet_info *vi)
 
 static void virtnet_rx_resume(struct virtnet_info *vi, struct receive_queue *rq)
 {
-	enable_delayed_refill(vi);
 	__virtnet_rx_resume(vi, rq, true);
 }
 
@@ -3845,10 +3767,6 @@ static int virtnet_close(struct net_device *dev)
 	struct virtnet_info *vi = netdev_priv(dev);
 	int i;
 
-	/* Make sure NAPI doesn't schedule refill work */
-	disable_delayed_refill(vi);
-	/* Make sure refill_work doesn't re-enable napi! */
-	cancel_delayed_work_sync(&vi->refill);
 	/* Prevent the config change callback from changing carrier
 	 * after close
 	 */
@@ -5804,7 +5722,6 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
-	enable_delayed_refill(vi);
 	enable_rx_mode_work(vi);
 
 	if (netif_running(vi->dev)) {
@@ -6561,7 +6478,6 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
 	if (!vi->rq)
 		goto err_rq;
 
-	INIT_DELAYED_WORK(&vi->refill, refill_work);
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		vi->rq[i].pages = NULL;
 		netif_napi_add_config(vi->dev, &vi->rq[i].napi, virtnet_poll,
@@ -6903,7 +6819,6 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
 	INIT_WORK(&vi->rx_mode_work, virtnet_rx_mode_work);
-	spin_lock_init(&vi->refill_lock);
 
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF)) {
 		vi->mergeable_rx_bufs = true;
@@ -7167,7 +7082,6 @@ static int virtnet_probe(struct virtio_device *vdev)
 	net_failover_destroy(vi->failover);
 free_vqs:
 	virtio_reset_device(vdev);
-	cancel_delayed_work_sync(&vi->refill);
 	free_receive_page_frags(vi);
 	virtnet_del_vqs(vi);
 free:
-- 
2.43.0

[PATCH net v3 3/3] virtio-net: clean up __virtnet_rx_pause/resume

[Bui Quang Minh]

The delayed refill worker is removed which makes virtnet_rx_pause/resume
quite the same as __virtnet_rx_pause/resume. So remove
__virtnet_rx_pause/resume and move the code to virtnet_rx_pause/resume.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
---
 drivers/net/virtio_net.c | 30 ++++++++++--------------------
 1 file changed, 10 insertions(+), 20 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index a4dbc958689b..745bae756920 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3369,8 +3369,8 @@ 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);
 
@@ -3385,17 +3385,12 @@ static void virtnet_rx_pause_all(struct virtnet_info *vi)
 	int i;
 
 	for (i = 0; i < vi->max_queue_pairs; i++)
-		__virtnet_rx_pause(vi, &vi->rq[i]);
+		virtnet_rx_pause(vi, &vi->rq[i]);
 }
 
-static void virtnet_rx_pause(struct virtnet_info *vi, struct receive_queue *rq)
-{
-	__virtnet_rx_pause(vi, rq);
-}
-
-static void __virtnet_rx_resume(struct virtnet_info *vi,
-				struct receive_queue *rq,
-				bool refill)
+static void virtnet_rx_resume(struct virtnet_info *vi,
+			      struct receive_queue *rq,
+			      bool refill)
 {
 	if (netif_running(vi->dev)) {
 		/* Pre-fill rq agressively, to make sure we are ready to get
@@ -3414,17 +3409,12 @@ static void virtnet_rx_resume_all(struct virtnet_info *vi)
 
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		if (i < vi->curr_queue_pairs)
-			__virtnet_rx_resume(vi, &vi->rq[i], true);
+			virtnet_rx_resume(vi, &vi->rq[i], true);
 		else
-			__virtnet_rx_resume(vi, &vi->rq[i], false);
+			virtnet_rx_resume(vi, &vi->rq[i], false);
 	}
 }
 
-static void virtnet_rx_resume(struct virtnet_info *vi, struct receive_queue *rq)
-{
-	__virtnet_rx_resume(vi, rq, true);
-}
-
 static int virtnet_rx_resize(struct virtnet_info *vi,
 			     struct receive_queue *rq, u32 ring_num)
 {
@@ -3438,7 +3428,7 @@ static int virtnet_rx_resize(struct virtnet_info *vi,
 	if (err)
 		netdev_err(vi->dev, "resize rx fail: rx queue index: %d err: %d\n", qindex, err);
 
-	virtnet_rx_resume(vi, rq);
+	virtnet_rx_resume(vi, rq, true);
 	return err;
 }
 
@@ -5811,7 +5801,7 @@ static int virtnet_rq_bind_xsk_pool(struct virtnet_info *vi, struct receive_queu
 
 	rq->xsk_pool = pool;
 
-	virtnet_rx_resume(vi, rq);
+	virtnet_rx_resume(vi, rq, true);
 
 	if (pool)
 		return 0;
-- 
2.43.0

Re: [PATCH net v3 1/3] virtio-net: don't schedule delayed refill worker

[Michael S. Tsirkin]

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 <minhquangbui99@gmail.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

and CC stable I think. Can you do that pls?

> ---
>  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

Re: [PATCH net v3 1/3] virtio-net: don't schedule delayed refill worker

[Bui Quang Minh]

On 1/6/26 22:29, Michael S. Tsirkin wrote:
> 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 <minhquangbui99@gmail.com>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
>
> and CC stable I think. Can you do that pls?

I've added Cc stable already.

Thanks for you review.

>
>> ---
>>   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

Re: [PATCH net v3 1/3] virtio-net: don't schedule delayed refill worker

[Jakub Kicinski]

On Tue,  6 Jan 2026 22:04:36 +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.

Happy to see this go FWIW. If it causes issues we should consider
adding some retry logic in the core (NAPI) rather than locally in
the driver..

> 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

The Closes should probably point to Paolo's report. We'll wipe these CI
logs sooner or later but the lore archive will stick around.

> @@ -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);

We should enforce _some_ minimal fill level at the time of open().
If the ring is completely empty no traffic will ever flow, right?
Perhaps I missed scheduling the NAPI somewhere..

>  		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);

Similar thing here? Tho not sure we can fail here..

> -	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);
> +

nit: spurious new line

> +		local_bh_enable();
> +	}
>  
>  	return 0;
>  }

Re: [PATCH net v3 1/3] virtio-net: don't schedule delayed refill worker

[Bui Quang Minh]

On 1/10/26 09:12, Jakub Kicinski wrote:
> On Tue,  6 Jan 2026 22:04:36 +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.
> Happy to see this go FWIW. If it causes issues we should consider
> adding some retry logic in the core (NAPI) rather than locally in
> the driver..
>
>> 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
> The Closes should probably point to Paolo's report. We'll wipe these CI
> logs sooner or later but the lore archive will stick around.

I'll fix it in the next version.

>
>> @@ -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);
> We should enforce _some_ minimal fill level at the time of open().
> If the ring is completely empty no traffic will ever flow, right?
> Perhaps I missed scheduling the NAPI somewhere..

The NAPI is enabled and scheduled in virtnet_napi_enable(). The code 
path is like this

virtnet_enable_queue_pair
-> virtnet_napi_enable
   -> virtnet_napi_do_enable
     -> virtqueue_napi_schedule

The same happens in __virtnet_rx_resume().

>
>>   		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);
> Similar thing here? Tho not sure we can fail here..
>
>> -	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);
>> +
> nit: spurious new line

I'll delete it in the next version.

>
>> +		local_bh_enable();
>> +	}
>>   
>>   	return 0;
>>   }

Re: [PATCH net v3 1/3] virtio-net: don't schedule delayed refill worker

[Michael S. Tsirkin]

On Fri, Jan 09, 2026 at 06:12:39PM -0800, Jakub Kicinski wrote:
> On Tue,  6 Jan 2026 22:04:36 +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.
> 
> Happy to see this go FWIW. If it causes issues we should consider
> adding some retry logic in the core (NAPI) rather than locally in
> the driver..
> 
> > 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
> 
> The Closes should probably point to Paolo's report. We'll wipe these CI
> logs sooner or later but the lore archive will stick around.
> 
> > @@ -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);
> 
> We should enforce _some_ minimal fill level at the time of open().
> If the ring is completely empty no traffic will ever flow, right?
> Perhaps I missed scheduling the NAPI somewhere..

Practically, single page allocations with GFP_KERNEL don't
really fail. So I think it's fine.

> >  		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);
> 
> Similar thing here? Tho not sure we can fail here..
> 
> > -	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);
> > +
> 
> nit: spurious new line
> 
> > +		local_bh_enable();
> > +	}
> >  
> >  	return 0;
> >  }

Re: [PATCH net v3 1/3] virtio-net: don't schedule delayed refill worker

[Jakub Kicinski]

On Sat, 10 Jan 2026 15:23:36 +0700 Bui Quang Minh wrote:
> >> @@ -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);  
> > We should enforce _some_ minimal fill level at the time of open().
> > If the ring is completely empty no traffic will ever flow, right?
> > Perhaps I missed scheduling the NAPI somewhere..  
> 
> The NAPI is enabled and scheduled in virtnet_napi_enable(). The code 
> path is like this
> 
> virtnet_enable_queue_pair
> -> virtnet_napi_enable  
>    -> virtnet_napi_do_enable
>      -> virtqueue_napi_schedule
> 
> The same happens in __virtnet_rx_resume().

I see. Alright, let me fix the nits while applying, no need to respin.
Kinda want this in the tree for a few days before shipping off to Linus.

Re: [PATCH net v3 0/3] virtio-net: fix the deadlock when disabling rx NAPI

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue,  6 Jan 2026 22:04:35 +0700 you wrote:
> Calling napi_disable() on an already disabled napi can cause the
> deadlock. In commit 4bc12818b363 ("virtio-net: disable delayed refill
> when pausing rx"), to avoid the deadlock, when pausing the RX in
> virtnet_rx_pause[_all](), we disable and cancel the delayed refill work.
> However, in the virtnet_rx_resume_all(), we enable the delayed refill
> work too early before enabling all the receive queue napis.
> 
> [...]

Here is the summary with links:
  - [net,v3,1/3] virtio-net: don't schedule delayed refill worker
    https://git.kernel.org/netdev/net/c/fcdef3bcbb2c
  - [net,v3,2/3] virtio-net: remove unused delayed refill worker
    https://git.kernel.org/netdev/net/c/1e7b90aa7988
  - [net,v3,3/3] virtio-net: clean up __virtnet_rx_pause/resume
    https://git.kernel.org/netdev/net/c/a0c159647e66

You are awesome, thank you!
-- 
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