Subject: [net-next-2.6 PATCH 3/3] net: consolidate netif_needs_gso() checks

From: Jeff Kirsher <[email-masked]>
Date: Wed, 17 Feb 2010 04:36:48 -0800

From: John Fastabend <[email-masked]>

netif_needs_gso() is checked twice in the TX path once,
before submitting the skb to the qdisc and once after
it is dequeued from the qdisc just before calling
ndo_hard_start().  This opens a window for a user to
change the gso/tso or tx checksum settings that can
cause netif_needs_gso to be true in one check and false
in the other.

Specifically, changing TX checksum setting may cause
the warning in skb_gso_segment() to be triggered if
the checksum is calculated earlier.

This consolidates the netif_needs_gso() calls so that
the stack only checks if gso is needed in
dev_hard_start_xmit().

Signed-off-by: John Fastabend <[email-masked]>
Signed-off-by: Jeff Kirsher <[email-masked]>
---

 net/core/dev.c |   50 +++++++++++++++++++++++++++++---------------------
 1 files changed, 29 insertions(+), 21 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index d1cf53d..84a0acb 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1835,12 +1835,40 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 {
 	const struct net_device_ops *ops = dev->netdev_ops;
 	int rc = NETDEV_TX_OK;
+	int need_gso = netif_needs_gso(dev, skb);
+
+	if (!need_gso) {
+		if (skb_has_frags(skb) &&
+		    !(dev->features & NETIF_F_FRAGLIST) &&
+		    __skb_linearize(skb))
+			goto out_kfree_skb;
+
+		/* Fragmented skb is linearized if device does not support SG,
+		 * or if at least one of fragments is in highmem and device
+		 * does not support DMA from it.
+		 */
+		if (skb_shinfo(skb)->nr_frags &&
+		    (!(dev->features & NETIF_F_SG) ||
+		      illegal_highdma(dev, skb)) &&
+		    __skb_linearize(skb))
+			goto out_kfree_skb;
+		/* If packet is not checksummed and device does not support
+		 * checksumming for this protocol, complete checksumming here.
+		 */
+		if (skb->ip_summed == CHECKSUM_PARTIAL) {
+			skb_set_transport_header(skb, skb->csum_start -
+				      skb_headroom(skb));
+			if (!dev_can_checksum(dev, skb) &&
+			     skb_checksum_help(skb))
+				goto out_kfree_skb;
+		}
+	}
 
 	if (likely(!skb->next)) {
 		if (!list_empty(&ptype_all))
 			dev_queue_xmit_nit(skb, dev);
 
-		if (netif_needs_gso(dev, skb)) {
+		if (need_gso) {
 			if (unlikely(dev_gso_segment(skb)))
 				goto out_kfree_skb;
 			if (skb->next)
@@ -2056,25 +2084,6 @@ int dev_queue_xmit(struct sk_buff *skb)
 	struct Qdisc *q;
 	int rc = -ENOMEM;
 
-	/* GSO will handle the following emulations directly. */
-	if (netif_needs_gso(dev, skb))
-		goto gso;
-
-	/* Convert a paged skb to linear, if required */
-	if (skb_needs_linearize(skb, dev) && __skb_linearize(skb))
-		goto out_kfree_skb;
-
-	/* If packet is not checksummed and device does not support
-	 * checksumming for this protocol, complete checksumming here.
-	 */
-	if (skb->ip_summed == CHECKSUM_PARTIAL) {
-		skb_set_transport_header(skb, skb->csum_start -
-					      skb_headroom(skb));
-		if (!dev_can_checksum(dev, skb) && skb_checksum_help(skb))
-			goto out_kfree_skb;
-	}
-
-gso:
 	/* Disable soft irqs for various locks below. Also
 	 * stops preemption for RCU.
 	 */
@@ -2133,7 +2142,6 @@ gso:
 	rc = -ENETDOWN;
 	rcu_read_unlock_bh();
 
-out_kfree_skb:
 	kfree_skb(skb);
 	return rc;
 out: