netdev - Re: [PATCH net-next 1/1] tcp: Prevent needless syn-ack rexmt during TWHS

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Date:	Thu, 25 Oct 2012 23:31:46 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Vijay Subramanian <subramanian.vijay@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Venkat Venkatsubra <venkat.x.venkatsubra@...cle.com>,
	Elliot Hughes <enh@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next 1/1] tcp: Prevent needless syn-ack rexmt during TWHS

On Thu, Oct 25, 2012 at 8:45 PM, Vijay Subramanian
<subramanian.vijay@...il.com> wrote:
> If server socket is slow to accept() connections, request_socks can represent
> connections for which the three-way handshake is already done.  From client's
> point of view, the connection is in ESTABLISHED state but on server side, socket
> is not in accept_queue or ESTABLISHED state.  When the syn-ack timer expires,
> because of the order in which tests are performed, server can retransmit the
> synack repeatedly. Following patch prevents the server from retransmitting the
> synack needlessly (and prevents client from replying with ack).  This reduces
> traffic when server is slow to accept() connections.
>
> If the server socket has received the third ack during connection establishment,
> this is remembered in inet_rsk(req)->acked.  The request_sock will expire in
> around 30 seconds and will be dropped if it does not move into accept_queue.
>
> With help from Eric Dumazet.
>
> Reported-by: Elliot Hughes <enh@...gle.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Vijay Subramanian <subramanian.vijay@...il.com>
> ---

Acked-by: Neal Cardwell <ncardwell@...gle.com>
Tested-by: Neal Cardwell <ncardwell@...gle.com>

Nice. Verified the bug and the fix.

neal
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