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

From: Neal Cardwell <ncardwell@google.com>
Date: Thu, 6 Dec 2012 14:50:58 -0500

On Thu, Dec 6, 2012 at 1:45 PM, Yuchung Cheng [off-list ref] wrote:

quoted

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 <redacted>
---

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

Applied.