netdev - Re: IPv6 kernel warning

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Message-ID: <CADVnQynJVvFesFYp68N5kzCJJD3-NXPZUUMfkg8m=or4eaLzMQ@mail.gmail.com>
Date:	Tue, 8 Oct 2013 10:05:51 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	dormando <dormando@...ia.net>,
	Michele Baldessari <michele@...syn.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	netdev <netdev@...r.kernel.org>,
	Nandita Dukkipati <nanditad@...gle.com>
Subject: Re: IPv6 kernel warning

On Mon, Oct 7, 2013 at 3:51 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
> I suspect tcp_process_tlp_ack() should not revert state to Open
> directly, but calling tcp_try_keep_open() instead, similar to all the
> undo processing in the tcp_fastretrans_alert(): after
> tcp_end_cwnd_reduction(), the process (E) falls back to check other
> stats before moving to CA_Open.
>
>
> index 9c62257..9012b42 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3314,7 +3314,7 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack,
>                         tcp_init_cwnd_reduction(sk, true);
>                         tcp_set_ca_state(sk, TCP_CA_CWR);
>                         tcp_end_cwnd_reduction(sk);
> -                       tcp_set_ca_state(sk, TCP_CA_Open);
> +                       tcp_try_keep_open(sk);
>                         NET_INC_STATS_BH(sock_net(sk),
>                                          LINUX_MIB_TCPLOSSPROBERECOVERY);
>                 }

Yes, nice catch! This looks good to me. My testing confirms that this
definitely fixes a bug when this code fires and there are segments
SACKed out. Since it will stay in CA_Disorder if there are outstanding
retransmissions, I bet it will also fix the WARN_ON(tp->retrans_out !=
0) in state TCP_CA_Open that people are seeing.

neal
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