netdev - Re: [PATCH net 4/4] virito-net: fix leaking page for gso packet during mergeable XDP

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Date:   Mon, 21 May 2018 18:01:36 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH net 4/4] virito-net: fix leaking page for gso packet
 during mergeable XDP

On Mon, May 21, 2018 at 04:35:06PM +0800, Jason Wang wrote:
> We need to drop refcnt to xdp_page if we see a gso packet. Otherwise
> it will be leaked. Fixing this by moving the check of gso packet above
> the linearizing logic.
> 
> Cc: John Fastabend <john.fastabend@...il.com>
> Fixes: 72979a6c3590 ("virtio_net: xdp, add slowpath case for non contiguous buffers")
> Signed-off-by: Jason Wang <jasowang@...hat.com>

typo in subject

> ---
>  drivers/net/virtio_net.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 165a922..f8db809 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -707,6 +707,14 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  		void *data;
>  		u32 act;
>  
> +		/* Transient failure which in theory could occur if
> +		 * in-flight packets from before XDP was enabled reach
> +		 * the receive path after XDP is loaded. In practice I
> +		 * was not able to create this condition.

BTW we should probably drop the last sentence. It says in theory, should be enough.

> +		 */
> +		if (unlikely(hdr->hdr.gso_type))
> +			goto err_xdp;
> +
>  		/* This happens when rx buffer size is underestimated
>  		 * or headroom is not enough because of the buffer
>  		 * was refilled before XDP is set. This should only
> @@ -728,14 +736,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			xdp_page = page;
>  		}
>  
> -		/* Transient failure which in theory could occur if
> -		 * in-flight packets from before XDP was enabled reach
> -		 * the receive path after XDP is loaded. In practice I
> -		 * was not able to create this condition.
> -		 */
> -		if (unlikely(hdr->hdr.gso_type))
> -			goto err_xdp;
> -
>  		/* Allow consuming headroom but reserve enough space to push
>  		 * the descriptor on if we get an XDP_TX return code.
>  		 */
> -- 
> 2.7.4