sunvnet: don't change gso data on clones

This patch unclones an skb for the case where the sunvnet driver needs to
change the segmentation size so that it doesn't interfere with TCP SACK's
use of them.
Signed-off-by: NDavid L Stevens <david.stevens@oracle.com>
Acked-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/sun/sunvnet.c

@@ -1192,23 +1192,16 @@ static int vnet_handle_offloads(struct vnet_port *port, struct sk_buff *skb)
 	skb_pull(skb, maclen);
 
 	if (port->tso && gso_size < datalen) {
+		if (skb_unclone(skb, GFP_ATOMIC))
+			goto out_dropped;
+
 		/* segment to TSO size */
 		skb_shinfo(skb)->gso_size = datalen;
 		skb_shinfo(skb)->gso_segs = gso_segs;
-
-		segs = skb_gso_segment(skb, dev->features & ~NETIF_F_TSO);
-
-		/* restore gso_size & gso_segs */
-		skb_shinfo(skb)->gso_size = gso_size;
-		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len - hlen,
-							 gso_size);
-	} else
-		segs = skb_gso_segment(skb, dev->features & ~NETIF_F_TSO);
-	if (IS_ERR(segs)) {
-		dev->stats.tx_dropped++;
-		dev_kfree_skb_any(skb);
-		return NETDEV_TX_OK;
 	}
+	segs = skb_gso_segment(skb, dev->features & ~NETIF_F_TSO);
+	if (IS_ERR(segs))
+		goto out_dropped;
 
 	skb_push(skb, maclen);
 	skb_reset_mac_header(skb);
@@ -1246,6 +1239,10 @@ static int vnet_handle_offloads(struct vnet_port *port, struct sk_buff *skb)
 	if (!(status & NETDEV_TX_MASK))
 		dev_kfree_skb_any(skb);
 	return status;
+out_dropped:
+	dev->stats.tx_dropped++;
+	dev_kfree_skb_any(skb);
+	return NETDEV_TX_OK;
 }
 
 static int vnet_start_xmit(struct sk_buff *skb, struct net_device *dev)