From 9e450c1ecb027417c99eba651413d2a6ba6ffc1f Mon Sep 17 00:00:00 2001
From: Yuchung Cheng <ycheng@google.com>
Date: Mon, 29 Apr 2019 15:46:15 -0700
Subject: [PATCH] tcp: better SYNACK sent timestamp
Detecting spurious SYNACK timeout using timestamp option requires
recording the exact SYNACK skb timestamp. Previously the SYNACK
sent timestamp was stamped slightly earlier before the skb
was transmitted. This patch uses the SYNACK skb transmission
timestamp directly.
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/ipv4/tcp_input.c | 2 +-
net/ipv4/tcp_output.c | 4 ++++
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 695f840acc14c..30c6a42b1f5b4 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6319,7 +6319,7 @@ static 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 = tcp_clock_us();
+ tcp_rsk(req)->snt_synack = 0;
tcp_rsk(req)->last_oow_ack_time = 0;
req->mss = rx_opt->mss_clamp;
req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 32061928b0542..0c4ed66dc1bf3 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3247,7 +3247,11 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
skb->skb_mstamp_ns = cookie_init_timestamp(req);
else
#endif
+ {
skb->skb_mstamp_ns = tcp_clock_ns();
+ if (!tcp_rsk(req)->snt_synack) /* Timestamp first SYNACK */
+ tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb);
+ }
#ifdef CONFIG_TCP_MD5SIG
rcu_read_lock();
--
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