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

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Date:   Mon, 18 Sep 2017 11:01:42 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Oleksandr Natalenko <oleksandr@...alenko.name>
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

On Mon, Sep 18, 2017 at 10:59 AM, Oleksandr Natalenko
<oleksandr@...alenko.name> wrote:
> OK. Should I keep FACK disabled?
Yes since it is disabled in the upstream by default. Although you can
experiment FACK enabled additionally.

Do we know the crash you first experienced is tied to this issue?

>
> On pondělí 18. září 2017 19:51:21 CEST Yuchung Cheng wrote:
>> Can you try this patch to verify my theory with tcp_recovery=0 and 1? thanks
>>
>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>> index 5af2f04f8859..9253d9ee7d0e 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -2381,6 +2381,7 @@ static void tcp_undo_cwnd_reduction(struct sock
>> *sk, bool unmark_loss)
>>         }
>>         tp->snd_cwnd_stamp = tcp_time_stamp;
>>         tp->undo_marker = 0;
>> +       WARN_ON(tp->retrans_out);
>>  }
>