netdev - Re: [PATCH net] tcp: only take RTT from timestamps if new data is acked

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Date:	Thu, 24 Oct 2013 12:55:37 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	davem@...emloft.net, ncardwell@...gle.com, edumazet@...gle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net] tcp: only take RTT from timestamps if new data is
 acked

On Thu, 2013-10-24 at 08:55 -0700, Yuchung Cheng wrote:
> Patch ed08495c3 "tcp: use RTT from SACK for RTO" has a bug that
> it does not check if the ACK acknowledge new data before taking
> the RTT sample from TCP timestamps. This patch adds the check
> back as required by the RFC.
> 
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> ---
>  net/ipv4/tcp_input.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 305cd05..6ffe41a 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -2856,7 +2856,8 @@ static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
>  	 * left edge of the send window.
>  	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
>  	 */
> -	if (seq_rtt < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
> +	if (seq_rtt < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
> +	    flag & FLAG_ACKED)
>  		seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
>  
>  	if (seq_rtt < 0)

Acked-by: Eric Dumazet <edumazet@...gle.com>



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