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Commit bc15afa3 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
Browse files

tcp: fix SYNACK RTT estimation in Fast Open 



tp->lsndtime may not always be the SYNACK timestamp if a passive
Fast Open socket sends data before handshake completes. And if the
remote acknowledges both the data and the SYNACK, the RTT sample
is already taken in tcp_ack(), so no need to call
tcp_update_ack_rtt() in tcp_synack_rtt_meas() aagain.

Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e9e2a904

net/ipv4/tcp_input.c

+13 −5
Original line number Diff line number Diff line
@@ -2871,13 +2871,18 @@ static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag, 
}



/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */

static void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)

static void tcp_synack_rtt_meas(struct sock *sk, const u32 synack_stamp)

{

	struct tcp_sock *tp = tcp_sk(sk);

	s32 seq_rtt = -1;



	if (tp->lsndtime && !tp->total_retrans)

		seq_rtt = tcp_time_stamp - tp->lsndtime;

	if (synack_stamp && !tp->total_retrans)

		seq_rtt = tcp_time_stamp - synack_stamp;



	/* If the ACK acks both the SYNACK and the (Fast Open'd) data packets

	 * sent in SYN_RECV, SYNACK RTT is the smooth RTT computed in tcp_ack()

	 */

	if (!tp->srtt)

		tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, seq_rtt, -1);

}
@@ -5587,6 +5592,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 
	struct request_sock *req;

	int queued = 0;

	bool acceptable;

	u32 synack_stamp;



	tp->rx_opt.saw_tstamp = 0;
@@ -5669,9 +5675,11 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 
		 * so release it.

		 */

		if (req) {

			synack_stamp = tcp_rsk(req)->snt_synack;

			tp->total_retrans = req->num_retrans;

			reqsk_fastopen_remove(sk, req, false);

		} else {

			synack_stamp = tp->lsndtime;

			/* Make sure socket is routed, for correct metrics. */

			icsk->icsk_af_ops->rebuild_header(sk);

			tcp_init_congestion_control(sk);
@@ -5694,7 +5702,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 
		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;

		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;

		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);

		tcp_synack_rtt_meas(sk, req);

		tcp_synack_rtt_meas(sk, synack_stamp);



		if (tp->rx_opt.tstamp_ok)

			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;