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

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Message-ID: <e8db28a3-61ae-4988-9ac6-ba67926056ab@gmail.com>
Date: Tue, 6 Jan 2026 22:39:09 +0700
From: Bui Quang Minh <minhquangbui99@...il.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: netdev@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>,
 Stanislav Fomichev <sdf@...ichev.me>, virtualization@...ts.linux.dev,
 linux-kernel@...r.kernel.org, bpf@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net v3 1/3] virtio-net: don't schedule delayed refill
 worker

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@...hat.com>
>> Closes: https://netdev-ctrl.bots.linux.dev/logs/vmksft/drv-hw-dbg/results/400961/3-xdp-py/stderr
>> Cc: stable@...r.kernel.org
>> Suggested-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> Acked-by: Michael S. Tsirkin <mst@...hat.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