This is a note to let you know that I've just added the patch titled
tcp: fix potential underestimation on rcv_rtt
to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: tcp-fix-potential-underestimation-on-rcv_rtt.patch and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Sun Dec 31 11:12:48 CET 2017
From: Wei Wang weiwan@google.com Date: Tue, 12 Dec 2017 16:28:58 -0800 Subject: tcp: fix potential underestimation on rcv_rtt
From: Wei Wang weiwan@google.com
[ Upstream commit 9ee11bd03cb1a5c3ca33c2bb70e7ed325f68890f ]
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: 645f4c6f2ebd ("tcp: switch rcv_rtt_est and rcvq_space to high resolution timestamps") Signed-off-by: Wei Wang weiwan@google.com Signed-off-by: Eric Dumazet edumazet@google.com Acked-by: Neal Cardwell ncardwell@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp_input.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -521,9 +521,6 @@ static void tcp_rcv_rtt_update(struct tc 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 @@ -560,6 +557,8 @@ static inline void tcp_rcv_rtt_measure(s 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: @@ -576,8 +575,11 @@ static inline void tcp_rcv_rtt_measure_t (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); } }
Patches currently in stable-queue which might be from weiwan@google.com are
queue-4.14/tcp-fix-potential-underestimation-on-rcv_rtt.patch