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

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Message-ID: <4b3bea7c-110d-48eb-bcf6-58f4b2cd1999@redhat.com>
Date: Thu, 3 Apr 2025 09:24:06 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Bui Quang Minh <minhquangbui99@...il.com>, 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>,
 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 7:42 AM, 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);

AFAICS at this point refill_work() could still be running, why don't you
need to call flush_delayed_work()?

@Jason: somewhat related, why virtnet_close() does not use
flush_delayed_work(), too?

Thanks,

Paolo