linux-kernel - Re: [PATCH] virtio-net: disable delayed refill when setting up xdp

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Message-ID: <8aad5ff9-6eab-411d-9569-9a2303561ac0@gmail.com>
Date: Thu, 3 Apr 2025 17:43:26 +0700
From: Bui Quang Minh <minhquangbui99@...il.com>
To: virtualization@...ts.linux.dev
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 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>,
 Eugenio Pérez <eperezma@...hat.com>,
 "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH] virtio-net: disable delayed refill when setting up xdp

On 4/2/25 12:42, Bui Quang Minh wrote:
> When setting up XDP for a running interface, 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. This can leads to deadlock
> when napi_disable() is called on an already disabled napi. This commit
> fixes this by disabling future and cancelling all inflight delayed
> refill works before calling napi_disabled() in virtnet_xdp_set.
>
> Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> ---
>   drivers/net/virtio_net.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7e4617216a4b..33406d59efe2 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -5956,6 +5956,15 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>   	if (!prog && !old_prog)
>   		return 0;
>   
> +	/*
> +	 * Make sure refill_work does not run concurrently to
> +	 * avoid napi_disable race which leads to deadlock.
> +	 */
> +	if (netif_running(dev)) {
> +		disable_delayed_refill(vi);
> +		cancel_delayed_work_sync(&vi->refill);
> +	}
> +
>   	if (prog)
>   		bpf_prog_add(prog, vi->max_queue_pairs - 1);
>   
> @@ -6004,6 +6013,8 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>   			virtnet_napi_tx_enable(&vi->sq[i]);
>   		}
>   	}
> +	if (netif_running(dev))
> +		enable_delayed_refill(vi);
While doing some testing, it look likes that we must call try_fill_recv 
to resume the rx path. I'll do more testing and send a new v2 patch.
>   
>   	return 0;
>   
> @@ -6019,6 +6030,7 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>   			virtnet_napi_enable(&vi->rq[i]);
>   			virtnet_napi_tx_enable(&vi->sq[i]);
>   		}
> +		enable_delayed_refill(vi);
>   	}
>   	if (prog)
>   		bpf_prog_sub(prog, vi->max_queue_pairs - 1);