netdev - Re: [REGRESSION] Warning in tcp_fastretrans_alert() of net/ipv4/tcp

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Date:   Tue, 19 Sep 2017 13:04:10 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Yuchung Cheng <ycheng@...gle.com>
Cc:     Neal Cardwell <ncardwell@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [REGRESSION] Warning in tcp_fastretrans_alert() of
 net/ipv4/tcp_input.c

Hi.

18.09.2017 23:40, Yuchung Cheng wrote:
> I assume this kernel does not have the patch that Neal proposed in his
> first reply?

Correct.

> The main warning needs to be triggered by another peculiar SACK that
> kicks the sender into recovery again (after undo). Please let it run
> longer if possible to see if we can get both. But the new data does
> indicate the we can (validly) be in CA_Open with retrans_out > 0.

OK, here it is:

===
» LC_TIME=C jctl -kb | grep RIP
…
Sep 19 12:54:03 defiant kernel: RIP: 
0010:tcp_undo_cwnd_reduction+0xbd/0xd0
Sep 19 12:54:22 defiant kernel: RIP: 
0010:tcp_undo_cwnd_reduction+0xbd/0xd0
Sep 19 12:54:25 defiant kernel: RIP: 
0010:tcp_undo_cwnd_reduction+0xbd/0xd0
Sep 19 12:56:00 defiant kernel: RIP: 
0010:tcp_fastretrans_alert+0x7c8/0x990
Sep 19 12:57:07 defiant kernel: RIP: 
0010:tcp_undo_cwnd_reduction+0xbd/0xd0
Sep 19 12:57:14 defiant kernel: RIP: 
0010:tcp_undo_cwnd_reduction+0xbd/0xd0
Sep 19 12:58:04 defiant kernel: RIP: 
0010:tcp_undo_cwnd_reduction+0xbd/0xd0
…
===

Note timestamps — two types of warning are distant in time, so didn't 
happen at once.

While still running this kernel, anything else I can check for you?