linux-kernel - Re: [PATCH net-next] virtio_net: Fix napi_skb_cache

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Message-ID: <dfd6b17e-ada5-41ce-8922-d97dd192ddb3@linux.alibaba.com>
Date: Mon, 15 Jul 2024 10:45:24 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Breno Leitao <leitao@...ian.org>
Cc: rbc@...a.com, horms@...nel.org,
 "open list:VIRTIO CORE AND NET DRIVERS" <virtualization@...ts.linux.dev>,
 "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>, "Michael S. Tsirkin"
 <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next] virtio_net: Fix napi_skb_cache_put warning


在 2024/7/12 下午7:53, Breno Leitao 写道:
> After the commit bdacf3e34945 ("net: Use nested-BH locking for
> napi_alloc_cache.") was merged, the following warning began to appear:
>
> 	 WARNING: CPU: 5 PID: 1 at net/core/skbuff.c:1451 napi_skb_cache_put+0x82/0x4b0
>
> 	  __warn+0x12f/0x340
> 	  napi_skb_cache_put+0x82/0x4b0
> 	  napi_skb_cache_put+0x82/0x4b0
> 	  report_bug+0x165/0x370
> 	  handle_bug+0x3d/0x80
> 	  exc_invalid_op+0x1a/0x50
> 	  asm_exc_invalid_op+0x1a/0x20
> 	  __free_old_xmit+0x1c8/0x510
> 	  napi_skb_cache_put+0x82/0x4b0
> 	  __free_old_xmit+0x1c8/0x510
> 	  __free_old_xmit+0x1c8/0x510
> 	  __pfx___free_old_xmit+0x10/0x10
>
> The issue arises because virtio is assuming it's running in NAPI context
> even when it's not, such as in the netpoll case.
>
> To resolve this, modify virtnet_poll_tx() to only set NAPI when budget
> is available. Same for virtnet_poll_cleantx(), which always assumed that
> it was in a NAPI context.
>
> Fixes: df133f3f9625 ("virtio_net: bulk free tx skbs")
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Breno Leitao <leitao@...ian.org>
> ---
>   drivers/net/virtio_net.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)

Reviewed-by: Heng Qi <hengqi@...ux.alibaba.com>

>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0b4747e81464..fb1331827308 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2341,7 +2341,7 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>   	return packets;
>   }
>   
> -static void virtnet_poll_cleantx(struct receive_queue *rq)
> +static void virtnet_poll_cleantx(struct receive_queue *rq, int budget)
>   {
>   	struct virtnet_info *vi = rq->vq->vdev->priv;
>   	unsigned int index = vq2rxq(rq->vq);
> @@ -2359,7 +2359,7 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
>   
>   		do {
>   			virtqueue_disable_cb(sq->vq);
> -			free_old_xmit(sq, txq, true);
> +			free_old_xmit(sq, txq, !!budget);
>   		} while (unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>   
>   		if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
> @@ -2404,7 +2404,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
>   	unsigned int xdp_xmit = 0;
>   	bool napi_complete;
>   
> -	virtnet_poll_cleantx(rq);
> +	virtnet_poll_cleantx(rq, budget);
>   
>   	received = virtnet_receive(rq, budget, &xdp_xmit);
>   	rq->packets_in_napi += received;
> @@ -2526,7 +2526,7 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
>   	txq = netdev_get_tx_queue(vi->dev, index);
>   	__netif_tx_lock(txq, raw_smp_processor_id());
>   	virtqueue_disable_cb(sq->vq);
> -	free_old_xmit(sq, txq, true);
> +	free_old_xmit(sq, txq, !!budget);
>   
>   	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
>   		if (netif_tx_queue_stopped(txq)) {