tcp: fix double-counted receiver RTT when leaving receiver fast path

We should not update ts_recent and call tcp_rcv_rtt_measure_ts() both
before and after going to step5. That wastes CPU and double-counts the
receiver-side RTT sample.

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

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a759e19..0d9bdac 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5485,6 +5485,9 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
                                if (tcp_checksum_complete_user(sk, skb))
                                        goto csum_error;
 
+                               if ((int)skb->truesize > sk->sk_forward_alloc)
+                                       goto step5;
+
                                /* Predicted packet is in window by definition.
                                 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
                                 * Hence, check seq<=rcv_wup reduces to:
@@ -5496,9 +5499,6 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 
                                tcp_rcv_rtt_measure_ts(sk, skb);
 
-                               if ((int)skb->truesize > sk->sk_forward_alloc)
-                                       goto step5;
-
                                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
 
                                /* Bulk data transfer: receiver */