From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleksandr Natalenko Subject: Re: [REGRESSION] Warning in tcp_fastretrans_alert() of net/ipv4/tcp_input.c Date: Fri, 15 Sep 2017 21:04:36 +0200 Message-ID: <12759907.teKvueDKTR@natalenko.name> References: <10035198.1vE6NFrMDO@natalenko.name> <1760119.uO98D2ft6f@natalenko.name> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Netdev , Yuchung Cheng To: Neal Cardwell Return-path: Received: from vulcan.natalenko.name ([104.207.131.136]:44670 "EHLO vulcan.natalenko.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751454AbdIOTEi (ORCPT ); Fri, 15 Sep 2017 15:04:38 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: Hello. With net.ipv4.tcp_fack set to 0 the warning still appears: =3D=3D=3D =C2=BB sysctl net.ipv4.tcp_fack =20 net.ipv4.tcp_fack =3D 0 =C2=BB LC_TIME=3DC dmesg -T | grep WARNING [Fri Sep 15 20:40:30 2017] WARNING: CPU: 1 PID: 711 at net/ipv4/tcp_input.c: 2826 tcp_fastretrans_alert+0x7c8/0x990 [Fri Sep 15 20:40:30 2017] WARNING: CPU: 0 PID: 711 at net/ipv4/tcp_input.c: 2826 tcp_fastretrans_alert+0x7c8/0x990 [Fri Sep 15 20:48:37 2017] WARNING: CPU: 1 PID: 711 at net/ipv4/tcp_input.c: 2826 tcp_fastretrans_alert+0x7c8/0x990 [Fri Sep 15 20:48:55 2017] WARNING: CPU: 0 PID: 711 at net/ipv4/tcp_input.c: 2826 tcp_fastretrans_alert+0x7c8/0x990 =C2=BB ps -up 711 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 711 4.3 0.0 0 0 ? S 18:12 7:23 [irq/123- enp3s0] =3D=3D=3D Any suggestions? On p=C3=A1tek 15. z=C3=A1=C5=99=C3=AD 2017 16:03:00 CEST Neal Cardwell wrot= e: > Thanks for testing that. That is a very useful data point. >=20 > I was able to cook up a packetdrill test that could put the connection > in CA_Disorder with retransmitted packets out, but not in CA_Open. So > we do not yet have a test case to reproduce this. >=20 > We do not see this warning on our fleet at Google. One significant > difference I see between our environment and yours is that it seems > you run with FACK enabled: >=20 > net.ipv4.tcp_fack =3D 1 >=20 > Note that FACK was disabled by default (since it was replaced by RACK) > between kernel v4.10 and v4.11. And this is exactly the time when this > bug started manifesting itself for you and some others, but not our > fleet. So my new working hypothesis would be that this warning is due > to a behavior that only shows up in kernels >=3D4.11 when FACK is > enabled. >=20 > Would you be able to disable FACK ("sysctl net.ipv4.tcp_fack=3D0" at > boot, or net.ipv4.tcp_fack=3D0 in /etc/sysctl.conf, or equivalent), > reboot, and test the kernel for a few days to see if the warning still > pops up? >=20 > thanks, > neal >=20 > [ps: apologies for the previous, mis-formatted post...]