gro: Avoid unnecessary comparison after skb_gro_header

For the overwhelming majority of cases, skb_gro_header's return
value cannot be NULL.  Yet we must check it because of its current
form.  This patch splits it up into multiple functions in order
to avoid this.

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

1 files changed, 16 insertions, 6 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 68342d431896..c3dcec5efea5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2518,20 +2518,30 @@ struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb)
         unsigned int thlen;
         unsigned int flags;
         unsigned int mss = 1;
+        unsigned int hlen;
+        unsigned int off;
         int flush = 1;
         int i;
 
-        th = skb_gro_header(skb, sizeof(*th));
-        if (unlikely(!th))
-                goto out;
+        off = skb_gro_offset(skb);
+        hlen = off + sizeof(*th);
+        th = skb_gro_header_fast(skb, off);
+        if (skb_gro_header_hard(skb, hlen)) {
+                th = skb_gro_header_slow(skb, hlen, off);
+                if (unlikely(!th))
+                        goto out;
+        }
 
         thlen = th->doff * 4;
         if (thlen < sizeof(*th))
                 goto out;
 
-        th = skb_gro_header(skb, thlen);
-        if (unlikely(!th))
-                goto out;
+        hlen = off + thlen;
+        if (skb_gro_header_hard(skb, hlen)) {
+                th = skb_gro_header_slow(skb, hlen, off);
+                if (unlikely(!th))
+                        goto out;
+        }
 
         skb_gro_pull(skb, thlen);