netdev - Re: [PATCH net-next v8 4/4] gve: Add support for raw addressing in the tx path

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Date:   Wed, 25 Nov 2020 19:12:27 +0100
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Awogbemila <awogbemila@...gle.com>, netdev@...r.kernel.org
Cc:     alexander.duyck@...il.com, saeed@...nel.org,
        Catherine Sullivan <csully@...gle.com>,
        Yangchun Fu <yangchun@...gle.com>
Subject: Re: [PATCH net-next v8 4/4] gve: Add support for raw addressing in
 the tx path



On 11/25/20 6:38 PM, David Awogbemila wrote:
> From: Catherine Sullivan <csully@...gle.com>
> 



> +	if (tx->raw_addressing)
> +		nsegs = gve_tx_add_skb_no_copy(priv, tx, skb);
> +	else
> +		nsegs = gve_tx_add_skb_copy(priv, tx, skb);
> +
> +	/* If the packet is getting sent, we need to update the skb */
> +	if (nsegs) {
> +		netdev_tx_sent_queue(tx->netdev_txq, skb->len);
> +		skb_tx_timestamp(skb);
> +
> +		/* Give packets to NIC. Even if this packet failed to send the doorbell
> +		 * might need to be rung because of xmit_more.
> +		 */
> +		tx->req += nsegs;
>  
> -	if (!netif_xmit_stopped(tx->netdev_txq) && netdev_xmit_more())
> -		return NETDEV_TX_OK;
> +		if (!netif_xmit_stopped(tx->netdev_txq) && netdev_xmit_more())
> +			return NETDEV_TX_OK;
>  
> -	gve_tx_put_doorbell(priv, tx->q_resources, tx->req);
> +		gve_tx_put_doorbell(priv, tx->q_resources, tx->req);
> +	}
>  	return NETDEV_TX_OK;
>  }
>

Code does not match the comment (Give packets to NIC.
    Even if this packet failed to send the doorbell
    might need to be rung because of xmit_more.)

You probably meant :

    if (nsegs) {
        netdev_tx_sent_queue(tx->netdev_txq, skb->len);
        skb_tx_timestamp(skb);
        tx->req += nsegs;
        if (!netif_xmit_stopped(tx->netdev_txq) && netdev_xmit_more())
            return NETDEV_TX_OK;
    }
    gve_tx_put_doorbell(priv, tx->q_resources, tx->req);
    return NETDEV_TX_OK;


Or

    if (nsegs) {
        netdev_tx_sent_queue(tx->netdev_txq, skb->len);
        skb_tx_timestamp(skb);
        tx->req += nsegs;
    }
    if (!netif_xmit_stopped(tx->netdev_txq) && netdev_xmit_more())
        return NETDEV_TX_OK;

    gve_tx_put_doorbell(priv, tx->q_resources, tx->req);
    return NETDEV_TX_OK;

Also you forgot to free the skb if it was not sent (in case of mapping error in gve_tx_add_skb_no_copy())

So you probably need to call dev_kfree_skb_any(), or risk leaking memory and freeze sockets.

    if (nsegs) {
        netdev_tx_sent_queue(tx->netdev_txq, skb->len);
        skb_tx_timestamp(skb);
        tx->req += nsegs;
    } else {
        dev_kfree_skb_any(skb);
    }
    if (!netif_xmit_stopped(tx->netdev_txq) && netdev_xmit_more())
        return NETDEV_TX_OK;

    gve_tx_put_doorbell(priv, tx->q_resources, tx->req);
    return NETDEV_TX_OK;