Re: [PATCH stable 1/2] virtio_net: fix error handling for mergeable buffers

[Jason Wang <jasowang@redhat.com>]

On 12/25/2013 10:56 PM, Michael S. Tsirkin wrote:
> Eric Dumazet noticed that if we encounter an error
> when processing a mergeable buffer, we don't
> dequeue all of the buffers from this packet,
> the result is almost sure to be loss of networking.
>
> Jason Wang noticed that we also leak a page and that we don't decrement
> the rq buf count, so we won't repost buffers (a resource leak).

This issue does not existed in stable tree.
> Fix both issues.
>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Michael Dalton <mwdalton@google.com>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: David S. Miller <davem@davemloft.net>
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>
> (cherry picked from commit 8fc3b9e9a229778e5af3aa453c44f1a3857ba769)
> ---
>  drivers/net/virtio_net.c | 66 +++++++++++++++++++++++++++++++++---------------
>  1 file changed, 46 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9fbdfcd..435076f 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -297,26 +297,33 @@ static struct sk_buff *page_to_skb(struct receive_queue *rq,
>  	return skb;
>  }
>  
> -static int receive_mergeable(struct receive_queue *rq, struct sk_buff *skb)
> +static struct sk_buff *receive_mergeable(struct net_device *dev,
> +					 struct receive_queue *rq,
> +					 void *buf,
> +					 unsigned int len)
>  {
> -	struct skb_vnet_hdr *hdr = skb_vnet_hdr(skb);
> -	struct page *page;
> -	int num_buf, i, len;
> +	struct skb_vnet_hdr *hdr = page_address(buf);
> +	int num_buf = hdr->mhdr.num_buffers;
> +	struct page *page = buf;
> +	struct sk_buff *skb = page_to_skb(rq, page, len);
> +	int i;
> +
> +	if (unlikely(!skb))
> +		goto err_skb;
>  
> -	num_buf = hdr->mhdr.num_buffers;
>  	while (--num_buf) {
>  		i = skb_shinfo(skb)->nr_frags;
>  		if (i >= MAX_SKB_FRAGS) {
>  			pr_debug("%s: packet too long\n", skb->dev->name);
>  			skb->dev->stats.rx_length_errors++;
> -			return -EINVAL;
> +			return NULL;
>  		}
>  		page = virtqueue_get_buf(rq->vq, &len);
>  		if (!page) {
> -			pr_debug("%s: rx error: %d buffers missing\n",
> -				 skb->dev->name, hdr->mhdr.num_buffers);
> -			skb->dev->stats.rx_length_errors++;
> -			return -EINVAL;
> +			pr_debug("%s: rx error: %d buffers %d missing\n",
> +				 dev->name, hdr->mhdr.num_buffers, num_buf);
> +			dev->stats.rx_length_errors++;
> +			goto err_buf;
>  		}
>  
>  		if (len > PAGE_SIZE)
> @@ -326,7 +333,25 @@ static int receive_mergeable(struct receive_queue *rq, struct sk_buff *skb)
>  
>  		--rq->num;
>  	}
> -	return 0;
> +	return skb;
> +err_skb:
> +	give_pages(rq, page);
> +	while (--num_buf) {
> +		buf = virtqueue_get_buf(rq->vq, &len);
> +		if (unlikely(!buf)) {
> +			pr_debug("%s: rx error: %d buffers missing\n",
> +				 dev->name, num_buf);
> +			dev->stats.rx_length_errors++;
> +			break;
> +		}
> +		page = buf;
> +		give_pages(rq, page);
> +		--rq->num;
> +	}
> +err_buf:
> +	dev->stats.rx_dropped++;
> +	dev_kfree_skb(skb);
> +	return NULL;
>  }
>  
>  static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
> @@ -354,17 +379,18 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
>  		skb_trim(skb, len);
>  	} else {
>  		page = buf;
> -		skb = page_to_skb(rq, page, len);
> -		if (unlikely(!skb)) {
> -			dev->stats.rx_dropped++;
> -			give_pages(rq, page);
> -			return;
> -		}
> -		if (vi->mergeable_rx_bufs)
> -			if (receive_mergeable(rq, skb)) {
> -				dev_kfree_skb(skb);
> +		if (vi->mergeable_rx_bufs) {
> +			skb = receive_mergeable(dev, rq, page, len);
> +			if (unlikely(!skb))
> +				return;
> +		} else {
> +			skb = page_to_skb(rq, page, len);
> +			if (unlikely(!skb)) {
> +				dev->stats.rx_dropped++;
> +				give_pages(rq, page);
>  				return;
>  			}
> +		}
>  	}
>  
>  	hdr = skb_vnet_hdr(skb);