netdev - Re: [PATCH] tcp: bug fix Fast Open client retransmission

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Message-ID: <CADVnQymE7ubywMytDCabQ=3gMWkp=gVrHZke0HpiufQNbF=1KQ@mail.gmail.com>
Date:	Thu, 6 Dec 2012 14:50:58 -0500
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] tcp: bug fix Fast Open client retransmission

On Thu, Dec 6, 2012 at 1:45 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
> If SYN-ACK partially acks SYN-data, the client retransmits the
> remaining data by tcp_retransmit_skb(). This increments lost recovery
> state variables like tp->retrans_out in Open state. If loss recovery
> happens before the retransmission is acked, it triggers the WARN_ON
> check in tcp_fastretrans_alert(). For example: the client sends
> SYN-data, gets SYN-ACK acking only ISN, retransmits data, sends
> another 4 data packets and get 3 dupacks.
>
> Since the retransmission is not caused by network drop it should not
> update the recovery state variables. Further the server may return a
> smaller MSS than the cached MSS used for SYN-data, so the retranmission
> needs a loop. Otherwise some data will not be retransmitted until timeout
> or other loss recovery events.
>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> ---

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