Re: [PATCH net] NTB: ntb_netdev: Preserve RX queue depth on allocation failure

[Dave Jiang <dave.jiang@intel.com>]

On 8/5/26 8:25 PM, Koichiro Den wrote:
> ntb_netdev_rx_handler() hands the received skb to the network stack
> before allocating its replacement. If the allocation fails, nothing is
> reposted. Every failure therefore takes one buffer out of the RX queue
> while the interface remains up, and enough failures eventually stall
> reception.
> 
> A retry path could refill the queue later, but ntb_netdev has none.
> Allocate the replacement first instead. If that fails, drop the packet
> and repost the same skb. This keeps the queue full and lets packet
> delivery resume as soon as memory is available again.
> 
> Fixes: 548c237c0a99 ("net: Add support for NTB virtual ethernet device")
> Cc: stable@vger.kernel.org
> Signed-off-by: Koichiro Den <den@valinux.co.jp>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  drivers/net/ntb_netdev.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ntb_netdev.c b/drivers/net/ntb_netdev.c
> index c3a6ba96fc8a..029a4a532a10 100644
> --- a/drivers/net/ntb_netdev.c
> +++ b/drivers/net/ntb_netdev.c
> @@ -127,8 +127,8 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data,
>  {
>  	struct ntb_netdev_queue *q = qp_data;
>  	struct ntb_netdev *dev = q->ntdev;
> +	struct sk_buff *skb, *new_skb;
>  	struct net_device *ndev;
> -	struct sk_buff *skb;
>  	int rc;
>  
>  	ndev = dev->ndev;
> @@ -144,6 +144,12 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data,
>  		goto enqueue_again;
>  	}
>  
> +	new_skb = netdev_alloc_skb(ndev, ndev->mtu + ETH_HLEN);
> +	if (!new_skb) {
> +		ndev->stats.rx_dropped++;
> +		goto enqueue_again;
> +	}
> +
>  	skb_put(skb, len);
>  	skb->protocol = eth_type_trans(skb, ndev);
>  	skb->ip_summed = CHECKSUM_NONE;
> @@ -157,12 +163,7 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data,
>  		ndev->stats.rx_bytes += len;
>  	}
>  
> -	skb = netdev_alloc_skb(ndev, ndev->mtu + ETH_HLEN);
> -	if (!skb) {
> -		ndev->stats.rx_errors++;
> -		ndev->stats.rx_frame_errors++;
> -		return;
> -	}
> +	skb = new_skb;
>  
>  enqueue_again:
>  	rc = ntb_transport_rx_enqueue(qp, skb, skb->data, ndev->mtu + ETH_HLEN);