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 <[email protected]> Signed-off-by: Neal Cardwell <[email protected]> Signed-off-by: Eric Dumazet <[email protected]> Signed-off-by: David S. Miller <[email protected]>
renliguo · May 1, 2019 · 9e450c1 · 9e450c1
1 parent 7c1f081
commit 9e450c1
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Showing 2 changed files with 5 additions and 1 deletion.
diff --git 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
@@ -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();