Re: [PATCH v3 1/3] virtio-net: disable delayed refill when pausing rx

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 15, 2025 at 02:43:39PM +0700, Bui Quang Minh wrote:
> 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()")
> Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>

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