tcp: consolidate SYNACK RTT sampling

The first patch consolidates SYNACK and other RTT measurement to use a
central function tcp_ack_update_rtt(). A (small) bonus is now SYNACK
RTT measurement happens after PAWS check, potentially reducing the
impact of RTO seeding on bad TCP timestamps values.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 6 deletions

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index ab1c08658528..58a3e69aef64 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -411,6 +411,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
                 tcp_enable_early_retrans(newtp);
                 newtp->tlp_high_seq = 0;
+                newtp->lsndtime = treq->snt_synack;
+                newtp->total_retrans = req->num_retrans;
 
                 /* So many TCP implementations out there (incorrectly) count the
                  * initial SYN frame in their delayed-ACK and congestion control
@@ -666,12 +668,6 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
         if (!(flg & TCP_FLAG_ACK))
                 return NULL;
 
-        /* Got ACK for our SYNACK, so update baseline for SYNACK RTT sample. */
-        if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr)
-                tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr;
-        else if (req->num_retrans) /* don't take RTT sample if retrans && ~TS */
-                tcp_rsk(req)->snt_synack = 0;
-
         /* For Fast Open no more processing is needed (sk is the
          * child socket).
          */