mv643xx_eth: fix race in trasmit path.

Because the socket buffer is freed in the completion interrupt, it is not
safe to access it after submitting it to the hardware.
Signed-off-by: NRichard Cochran <richard.cochran@omicron.at>
Acked-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/mv643xx_eth.c

@@ -859,7 +859,7 @@ static int txq_submit_skb(struct tx_queue *txq, struct sk_buff *skb)
 static netdev_tx_t mv643xx_eth_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct mv643xx_eth_private *mp = netdev_priv(dev);
-	int queue;
+	int length, queue;
 	struct tx_queue *txq;
 	struct netdev_queue *nq;
 
@@ -881,10 +881,12 @@ static netdev_tx_t mv643xx_eth_xmit(struct sk_buff *skb, struct net_device *dev)
 		return NETDEV_TX_OK;
 	}
 
+	length = skb->len;
+
 	if (!txq_submit_skb(txq, skb)) {
 		int entries_left;
 
-		txq->tx_bytes += skb->len;
+		txq->tx_bytes += length;
 		txq->tx_packets++;
 
 		entries_left = txq->tx_ring_size - txq->tx_desc_count;