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Date: Wed, 24 Aug 2011 21:03:07 +0200 From: Alexander Zimmermann <alexander.zimmermann@...sys.rwth-aachen.de> To: Eric Dumazet <eric.dumazet@...il.com> Cc: netdev <netdev@...r.kernel.org>, Jerry Chu <hkchu@...gle.com>, Lukowski Damian <damian@....rwth-aachen.de>, Hannemann Arnd <arnd@...dnet.de> Subject: Re: [BUG] tcp : how many times a frame can possibly be retransmitted ? Hi Eric, Am 24.08.2011 um 18:21 schrieb Eric Dumazet: > On one dev machine running net-next, I just found strange tcp sessions > that retransmit a frame forever (The other peer disappeared) not forever... If remember correctly you will stop after 120s. > > # ss -emoi dst 10.2.1.1 > State Recv-Q Send-Q Local Address:Port Peer Address:Port > ESTAB 0 816 10.2.1.2:37930 10.2.1.1:ssh timer:(on,630ms,246) ino:60786 sk:ffff8801189aa400 > mem:(r0,w3776,f320,t0) ts sack ecn cubic wscale:8,6 rto:1680 rtt:16.25/7.5 ato:40 ssthresh:7 send 1.4Mbps rcv_rtt:10 rcv_space:16632 > > > You can see the retransmit count : 246 > > What possibly can be going on ? > > What happened to backoff ? > > # grep . /proc/sys/net/ipv4/tcp_retries* > /proc/sys/net/ipv4/tcp_retries1:3 > /proc/sys/net/ipv4/tcp_retries2:15 > > > > extract of tcpdump : > > 12:01:02.074244 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16128024 59389> > 12:01:03.754243 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16128192 59389> > 12:01:05.434245 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16128360 59389> > 12:01:07.114243 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16128528 59389> > 12:01:08.794248 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16128696 59389> > 12:01:10.474242 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16128864 59389> > 12:01:12.154243 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16129032 59389> > 12:01:13.834241 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16129200 59389> > 12:01:15.514246 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16129368 59389> > 12:01:17.194244 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16129536 59389> > 12:01:18.874248 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16129704 59389> > 12:01:20.554243 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16129872 59389> > 12:01:22.234244 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16130040 59389> > 12:01:23.914244 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16130208 59389> > 12:01:25.594247 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16130376 59389> > 12:01:27.274242 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16130544 59389> > 12:01:28.954242 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16130712 59389> > 12:01:30.634248 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16130880 59389> > 12:01:32.314245 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16131048 59389> > 12:01:33.994243 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16131216 59389> > 12:01:35.674250 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16131384 59389> > 12:01:37.354244 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16131552 59389> > 12:01:39.034245 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16131720 59389> > 12:01:40.714245 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16131888 59389> > 12:01:42.394245 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16132056 59389> > 12:01:44.074242 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16132224 59389> > 12:01:45.754249 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16132392 59389> > 12:01:47.434242 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16132560 59389> > 12:01:49.114247 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16132728 59389> > 12:01:50.794250 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16132896 59389> > 12:01:52.474247 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16133064 59389> > 12:01:54.154242 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16133232 59389> > 12:01:55.834246 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16133400 59389> > 12:01:57.514243 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16133568 59389> > 12:01:59.194247 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16133736 59389> > 12:02:00.874250 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16133904 59389> > 12:02:02.554242 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16134072 59389> > 12:02:04.234243 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16134240 59389> > 12:02:05.914245 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16134408 59389> > 12:02:07.594244 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16134576 59389> > 12:02:09.274249 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16134744 59389> > 12:02:10.954241 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16134912 59389> > 12:02:12.634249 IP 10.2.1.2.37930 > 10.2.1.1.ssh: P 0:144(144) ack 1 win 1002 <nop,nop,timestamp 16135080 59389> > > tcp_retransmit_timer() does the exponential backoff, but something > resets icsk_rto to a low value ? > > Ah, it seems to be because of commit f1ecd5d9e7366609 > (Revert Backoff [v3]: Revert RTO on ICMP destination unreachable) > > Since arp resolution (or routing, I dont know yet) fails, an > internal/loopback ICMP host/network unreachable message is > generated and handled in tcp_v4_err() : Yeah, you have a local connectivity disruption. This is one possible scenario. > > icsk_backoff-- and icsk_rto is reset. > > I am afraid this can generate a storm (cpu time at very least), > in case we have many tcp sessions in this state. Hmm, maybe. I don't know. Arnd or Damian what are you thing about this point? > > I guess its time for me to read RFC 6069 If you find a bug. Let me know. Alex > > > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html // // Dipl.-Inform. Alexander Zimmermann // Department of Computer Science, Informatik 4 // RWTH Aachen University // Ahornstr. 55, 52056 Aachen, Germany // phone: (49-241) 80-21422, fax: (49-241) 80-22222 // email: zimmermann@...rwth-aachen.de // web: http://www.umic-mesh.net // -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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