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/include/net/tcp.h b/include/net/tcp.h
index a718d0e3d8e785af5deea49d4b9fd23f768773ae..6feeccd83dd7557abd30e32c0547f483b79bd238 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1125,6 +1125,7 @@ static inline void tcp_openreq_init(struct request_sock *req,
        req->cookie_ts = 0;
        tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
        tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+       tcp_rsk(req)->snt_synack = 0;
        req->mss = rx_opt->mss_clamp;
        req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
        ireq->tstamp_ok = rx_opt->tstamp_ok;

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e2bec815ff23bfa31eb2f7b3aec40b018e397f22..bb326684495bc3af0cee5d2b580d5f79b7e9e9c9 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5983,6 +5983,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                                 * need req so release it.
                                 */
                                if (req) {
+                                       tcp_synack_rtt_meas(sk, req);
                                        reqsk_fastopen_remove(sk, req, false);
                                } else {
                                        /* Make sure socket is routed, for

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 1e66f7fb4fe6787bdefeabb2896fb4d3af56857d..0a7e020f16b58ac7bd06db3dce0724e7947362c7 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -868,6 +868,8 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
                                            ireq->rmt_addr,
                                            ireq->opt);
                err = net_xmit_eval(err);
+               if (!tcp_rsk(req)->snt_synack && !err)
+                       tcp_rsk(req)->snt_synack = tcp_time_stamp;
        }
 
        return err;
@@ -1382,6 +1384,7 @@ static int tcp_v4_conn_req_fastopen(struct sock *sk,
        struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
        const struct inet_request_sock *ireq = inet_rsk(req);
        struct sock *child;
+       int err;
 
        req->retrans = 0;
        req->sk = NULL;
@@ -1393,8 +1396,11 @@ static int tcp_v4_conn_req_fastopen(struct sock *sk,
                kfree_skb(skb_synack);
                return -1;
        }
-       ip_build_and_send_pkt(skb_synack, sk, ireq->loc_addr,
-                       ireq->rmt_addr, ireq->opt);
+       err = ip_build_and_send_pkt(skb_synack, sk, ireq->loc_addr,
+                                   ireq->rmt_addr, ireq->opt);
+       err = net_xmit_eval(err);
+       if (!err)
+               tcp_rsk(req)->snt_synack = tcp_time_stamp;
        /* XXX (TFO) - is it ok to ignore error and continue? */
 
        spin_lock(&queue->fastopenq->lock);
@@ -1612,7 +1618,6 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
                isn = tcp_v4_init_sequence(skb);
        }
        tcp_rsk(req)->snt_isn = isn;
-       tcp_rsk(req)->snt_synack = tcp_time_stamp;
 
        if (dst == NULL) {
                dst = inet_csk_route_req(sk, &fl4, req);
@@ -1650,6 +1655,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
                if (err || want_cookie)
                        goto drop_and_free;
 
+               tcp_rsk(req)->snt_synack = tcp_time_stamp;
                tcp_rsk(req)->listener = NULL;
                /* Add the request_sock to the SYN table */
                inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index cfeeeb7fcf54905fa522b0489923b574804298e2..d6212d6bc8d89a5a3429329e78ee36fb4c384d2d 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1169,7 +1169,6 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
        }
 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 @@ have_isn:
            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;