Re: [PATCH] amd-xgbe: set skb to NULL after freeing it

[David Miller]

From: Pan Bian <bianpan2...@163.com>
Date: Wed, 28 Nov 2018 16:09:45 +0800

> @@ -2754,6 +2754,7 @@ static int xgbe_rx_poll(struct xgbe_channel *channel, 
> int budget)
>                               netif_err(pdata, rx_err, netdev,
>                                         "error in received packet\n");
>                       dev_kfree_skb(skb);
> +                     skb = NULL;
>                       goto next_packet;
>               }
>  
> @@ -2806,6 +2807,7 @@ static int xgbe_rx_poll(struct xgbe_channel *channel, 
> int budget)
>                       netif_err(pdata, rx_err, netdev,
>                                 "packet length exceeds configured MTU\n");
>                       dev_kfree_skb(skb);
> +                     skb = NULL;
>                       goto next_packet;
>               }
>  
> -- 
> 2.7.4

If either of these two cases are executed, it means that it must be
the case that:

        !last || context_next

is FALSE, therefore the conditional in the tail code of this function:

        /* Check if we need to save state before leaving */
        if (received && (!last || context_next)) {
                rdata = XGBE_GET_DESC_DATA(ring, ring->cur);
                rdata->state_saved = 1;
                rdata->state.skb = skb;
                rdata->state.len = len;
                rdata->state.error = error;
        }

will not trigger, and therefore we will not record the free'd SKB.

And if we iterate the loop again, it is guaranteed that 'skb' will
be set to a new packet or NULL.

So there is no problem here.