[NET]: Avoid allocating skb in skb_pad

First of all it is unnecessary to allocate a new skb in skb_pad since
the existing one is not shared.  More importantly, our hard_start_xmit
interface does not allow a new skb to be allocated since that breaks
requeueing.

This patch uses pskb_expand_head to expand the existing skb and linearize
it if needed.  Actually, someone should sift through every instance of
skb_pad on a non-linear skb as they do not fit the reasons why this was
originally created.

Incidentally, this fixes a minor bug when the skb is cloned (tcpdump,
TCP, etc.).  As it is skb_pad will simply write over a cloned skb.  Because
of the position of the write it is unlikely to cause problems but still
it's best if we don't do it.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 7 deletions

diff --git a/drivers/net/yellowfin.c b/drivers/net/yellowfin.c
index fd0f43b..ecec8e5 100644
--- a/drivers/net/yellowfin.c
+++ b/drivers/net/yellowfin.c
@@ -862,13 +862,11 @@ static int yellowfin_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		/* Fix GX chipset errata. */
 		if (cacheline_end > 24  || cacheline_end == 0) {
 			len = skb->len + 32 - cacheline_end + 1;
-			if (len != skb->len)
-				skb = skb_padto(skb, len);
-		}
-		if (skb == NULL) {
-			yp->tx_skbuff[entry] = NULL;
-			netif_wake_queue(dev);
-			return 0;
+			if (skb_padto(skb, len)) {
+				yp->tx_skbuff[entry] = NULL;
+				netif_wake_queue(dev);
+				return 0;
+			}
 		}
 	}
 	yp->tx_skbuff[entry] = skb;