From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH] net: dwc-xlgmac: set skb to NULL after freeing it
Date: Wed, 28 Nov 2018 10:59:06 -0800 (PST)
Message-ID: <20181128.105906.2127945279482643879.davem@davemloft.net>
References: <1543396853-35188-1-git-send-email-bianpan2016@163.com>
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Cc: Jose.Abreu@synopsys.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
To: bianpan2016@163.com
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From: Pan Bian <bianpan2016@163.com>
Date: Wed, 28 Nov 2018 17:20:53 +0800

> @@ -1180,6 +1180,7 @@ static int xlgmac_rx_poll(struct xlgmac_channel *channel, int budget)
>  				netif_err(pdata, rx_err, netdev,
>  					  "error in received packet\n");
>  			dev_kfree_skb(skb);
> +			skb = NULL;
>  			goto next_packet;
>  		}
>  
> @@ -1227,6 +1228,7 @@ static int xlgmac_rx_poll(struct xlgmac_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;
>  		}

Same problem as your amd-xgbe patch, the condition you say can occurr is
actually impossible.