[TCP]: rare bad TCP checksum with 2.6.19

The patch "Replace CHECKSUM_HW by CHECKSUM_PARTIAL/CHECKSUM_COMPLETE"
changed to unconditional copying of ip_summed field from collapsed
skb. This patch reverts this change.

The majority of substantial work including heavy testing
and diagnosing by: Michael Tokarev <mjt@tls.msk.ru>
Possible reasons pointed by: Herbert Xu and Patrick McHardy.

Signed-off-by: Jarek Poplawski <jarkao2@o2.pl>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 32c1a972fa31..23e32c806916 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1650,7 +1650,8 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int m
 
                 memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size);
 
-                skb->ip_summed = next_skb->ip_summed;
+                if (next_skb->ip_summed == CHECKSUM_PARTIAL)
+                        skb->ip_summed = CHECKSUM_PARTIAL;
 
                 if (skb->ip_summed != CHECKSUM_PARTIAL)
                         skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);