netdev - Re: [PATCH net v4 3/3] net: hns: fixed bug that skb used after kfree

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Message-ID: <eb7eaead-f32c-0ffb-3b24-0d6e11a60843@gmail.com>
Date:   Thu, 27 Apr 2017 10:38:29 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Yankejian <yankejian@...wei.com>, davem@...emloft.net,
        salil.mehta@...wei.com, yisen.zhuang@...wei.com,
        matthias.bgg@...il.com, lipeng321@...wei.com, zhouhuiru@...wei.com,
        huangdaode@...ilicon.com
Cc:     netdev@...r.kernel.org, linuxarm@...wei.com
Subject: Re: [PATCH net v4 3/3] net: hns: fixed bug that skb used after kfree

On 04/26/2017 07:44 PM, Yankejian wrote:
>  	struct hns_nic_priv *priv = netdev_priv(ndev);
>  	struct hnae_ring *ring = ring_data->ring;
> @@ -361,6 +361,10 @@ int hns_nic_net_xmit_hw(struct net_device *ndev,
>  	dev_queue = netdev_get_tx_queue(ndev, skb->queue_mapping);
>  	netdev_tx_sent_queue(dev_queue, skb->len);
>  
> +	netif_trans_update(ndev);
> +	ndev->stats.tx_bytes += skb->len;
> +	ndev->stats.tx_packets++;

This is still wrong though, you should not update your TX statistics
until you get a TX completion interrupt that confirms these packets were
actually transmitted. This has the advantage of not causing use after
free in your ndo_start_xmit() function (current bug), and also allows
feeding information into BQL where it is appropriate, and in a central
location: the TX completion handler.
-- 
Florian