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Commit 9ee11bd0 authored by Wei Wang's avatar Wei Wang Committed by David S. Miller
Browse files

tcp: fix potential underestimation on rcv_rtt 



When ms timestamp is used, current logic uses 1us in
tcp_rcv_rtt_update() when the real rcv_rtt is within 1 - 999us.
This could cause rcv_rtt underestimation.
Fix it by always using a min value of 1ms if ms timestamp is used.

Fixes: 645f4c6f ("tcp: switch rcv_rtt_est and rcvq_space to high resolution timestamps")
Signed-off-by: default avatarWei Wang <weiwan@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c009cb84

net/ipv4/tcp_input.c

+6 −4
Original line number Diff line number Diff line
@@ -508,9 +508,6 @@ static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep) 
	u32 new_sample = tp->rcv_rtt_est.rtt_us;

	long m = sample;



	if (m == 0)

		m = 1;



	if (new_sample != 0) {

		/* If we sample in larger samples in the non-timestamp

		 * case, we could grossly overestimate the RTT especially
@@ -547,6 +544,8 @@ static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp) 
	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))

		return;

	delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);

	if (!delta_us)

		delta_us = 1;

	tcp_rcv_rtt_update(tp, delta_us, 1);



new_measure:
@@ -563,8 +562,11 @@ static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, 
	    (TCP_SKB_CB(skb)->end_seq -

	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss)) {

		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;

		u32 delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);

		u32 delta_us;



		if (!delta)

			delta = 1;

		delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);

		tcp_rcv_rtt_update(tp, delta_us, 0);

	}

}