netdev - Re: [PATCH] tcp: fix infinite cwnd in tcp_complete

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Date:	Sun, 29 Apr 2012 23:49:01 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	davem@...emloft.net, ilpo.jarvinen@...sinki.fi,
	nanditad@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: fix infinite cwnd in tcp_complete_cwr()

On Sat, Apr 28, 2012 at 3:04 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
> When the cwnd reduction is done, ssthresh may be infinite
> if TCP enters CWR via ECN or F-RTO. If cwnd is not undone, i.e.,
> undo_marker is set, tcp_complete_cwr() falsely set cwnd to the
> infinite ssthresh value. The correct operation is to keep cwnd
> intact because it has been updated in ECN or F-RTO.
>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> ---
>  net/ipv4/tcp_input.c |    8 +++++---
>  1 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index c93b0cb..ac417de 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -2868,11 +2868,13 @@ static inline void tcp_complete_cwr(struct sock *sk)
>
>        /* Do not moderate cwnd if it's already undone in cwr or recovery. */
>        if (tp->undo_marker) {
> -               if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR)
> +               if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) {
>                        tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);

In this TCP_CA_CWR case the patch needs to add the assignment:

     tp->snd_cwnd_stamp = tcp_time_stamp;

I know that was in earlier versions of your patch; looks like it just
got accidentally dropped on this latest version.

Otherwise, looks good to me.

neal
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