tcp: TCP Fast Open Server - take SYNACK RTT after completing 3WHS
When taking SYNACK RTT samples for servers using TCP Fast Open, fix
the code to ensure that we only call tcp_valid_rtt_meas() after we
receive the ACK that completes the 3-way handshake.
Previously we were always taking an RTT sample in
tcp_v4_syn_recv_sock(). However, for TCP Fast Open connections
tcp_v4_conn_req_fastopen() calls tcp_v4_syn_recv_sock() at the time we
receive the SYN. So for TFO we must wait until tcp_rcv_state_process()
to take the RTT sample.
To fix this, we wait until after TFO calls tcp_v4_syn_recv_sock()
before we set the snt_synack timestamp, since tcp_synack_rtt_meas()
already ensures that we only take a SYNACK RTT sample if snt_synack is
non-zero. To be careful, we only take a snt_synack timestamp when
a SYNACK transmit or retransmit succeeds.
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index cfeeeb7..d6212d6b 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1169,7 +1169,6 @@
}
have_isn:
tcp_rsk(req)->snt_isn = isn;
- tcp_rsk(req)->snt_synack = tcp_time_stamp;
if (security_inet_conn_request(sk, skb, req))
goto drop_and_release;
@@ -1180,6 +1179,7 @@
want_cookie)
goto drop_and_free;
+ tcp_rsk(req)->snt_synack = tcp_time_stamp;
tcp_rsk(req)->listener = NULL;
inet6_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
return 0;