netdev - Re: [PATCH] tcp: fixing TLP's FIN recovery

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Date:	Mon, 09 Jun 2014 11:33:12 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Per Hurtig <per.hurtig@....se>
Cc:	Nandita Dukkipati <nanditad@...gle.com>,
	Netdev <netdev@...r.kernel.org>,
	Anna Brunström <anna.brunstrom@....se>,
	mohammad.rajiullah@....se, Neal Cardwell <ncardwell@...gle.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Subject: Re: [PATCH] tcp: fixing TLP's FIN recovery

On Mon, 2014-06-09 at 09:24 -0700, Eric Dumazet wrote:

> Hmm... We hit this point... This is embarrassing I guess.
> 
>        if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
>                 return -EHOSTUNREACH; /* Routing failure or similar. */

False alarm. This was caused of route being dismantled at the end of the
test, and a dangling socket tried to retransmit.

The 25ms timer I had was caused by early retransmit (25 ms = RTT/4 in my
test), because only one packet was missing.

Following test runs fine, as 3 packets are missing.

// Establish a connection.
0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
0.000 bind(3, ..., ...) = 0
0.000 listen(3, 1) = 0

0.100 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
0.100 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 6>
0.200 < . 1:1(0) ack 1 win 257
0.200 accept(3, ..., ...) = 4

// Send 8 MSS.
0.200 write(4, ..., 8000) = 8000
+.000 > P. 1:8001(8000) ack 1
+.000   close(4) = 0
+.000 > F. 8001:8001(0) ack 1

// Receiver ACKs 5 packets
0.300 < . 1:1(0) ack 5001 win 257
// Check if TLP is triggering, even if last packet is a pure FIN
0.500 > F. 8001:8001(0) ack 1

0.610 < . 1:1(0) ack 5001 win 257 <sack 8001:8002,nop,nop>
0.610 > . 5001:6001(1000) ack 1
0.610 > . 6001:7001(1000) ack 1

0.710 < . 1:1(0) ack 7001 win 257 <sack 8001:8002,nop,nop>
0.710 > P. 7001:8001(1000) ack 1

0.810 < . 1:1(0) ack 8002 win 257




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