udp: avoid csum_partial() for validated skb

In commit e6afc8ace6dd5 ("udp: remove headers from UDP packets before
queueing"), udp_csum_pull_header() helper was added but missed fact
that CHECKSUM_UNNECESSARY packets were now converted to CHECKSUM_NONE
and skb->csum_valid was set to 1 for them.

Since csum_partial() is quite expensive, even for 8-byte area, it is
worth adding a test.

We also can use skb->data instead of udp_hdr() as we are pulling
UDP headers, as it is sightly faster.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/udp.h b/include/net/udp.h
index ae07f37..8894d71 100644 (file)
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -160,8 +160,8 @@ void udp_set_csum(bool nocheck, struct sk_buff *skb,
 
 static inline void udp_csum_pull_header(struct sk_buff *skb)
 {
-       if (skb->ip_summed == CHECKSUM_NONE)
-               skb->csum = csum_partial(udp_hdr(skb), sizeof(struct udphdr),
+       if (!skb->csum_valid && skb->ip_summed == CHECKSUM_NONE)
+               skb->csum = csum_partial(skb->data, sizeof(struct udphdr),
                                         skb->csum);
        skb_pull_rcsum(skb, sizeof(struct udphdr));
        UDP_SKB_CB(skb)->cscov -= sizeof(struct udphdr);