tcp: do not enqueue skb with SYN flag

If we remove the SYN flag from the skbs that tcp_fastopen_add_skb()
places in socket receive queue, then we can remove the test that
tcp_recvmsg() has to perform in fast path.

All we have to do is to adjust SEQ in the slow path.

For the moment, we place an unlikely() and output a message
if we find an skb having SYN flag set.
Goal would be to get rid of the test completely.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 19746b3fcbbe..c5075779e017 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1466,8 +1466,10 @@ static struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off)
 
         while ((skb = skb_peek(&sk->sk_receive_queue)) != NULL) {
                 offset = seq - TCP_SKB_CB(skb)->seq;
-                if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
+                if (unlikely(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
+                        pr_err_once("%s: found a SYN, please report !\n", __func__);
                         offset--;
+                }
                 if (offset < skb->len || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)) {
                         *off = offset;
                         return skb;
@@ -1657,8 +1659,10 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
                                 break;
 
                         offset = *seq - TCP_SKB_CB(skb)->seq;
-                        if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
+                        if (unlikely(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
+                                pr_err_once("%s: found a SYN, please report !\n", __func__);
                                 offset--;
+                        }
                         if (offset < skb->len)
                                 goto found_ok_skb;
                         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)