Re: [PATCH net v2 1/3] virtio-net: don't schedule delayed refill worker

[Bui Quang Minh <minhquangbui99@gmail.com>]

On 1/3/26 23:57, Michael S. Tsirkin wrote:
> On Fri, Jan 02, 2026 at 10:20:21PM +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
>> 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 <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 | 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);
>>   	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
> hmm do we even need this, then?
>
>> +			 */
>> +			try_fill_recv(vi, &vi->rq[i], GFP_KERNEL);
>>   
>>   		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);
>
> hmm do we even need this, then?
>
>> +
>>   	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)
>> @@ -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.
>> +		 */
> I'd drop this comment, it does not clarify much.

Here I want to note on why we can't use try_fill_recv like in other places.

>
>> +		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