From 705d06b289e9821439b7b694d766cad75bc064e5 Mon Sep 17 00:00:00 2001
From: Michael Tuexen <tuexen@FreeBSD.org>
Date: Fri, 5 Mar 2021 15:57:26 +0100
Subject: [PATCH] rack: unbreak TCP fast open for the client side

Allow sending user data on the SYN segment.

Reviewed by:		rrs
MFC after:		3 days
Differential Revision:	https://reviews.freebsd.org/D29082
Sponsored by:		Netflix, Inc.
---
 sys/netinet/tcp_stacks/rack.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/netinet/tcp_stacks/rack.c b/sys/netinet/tcp_stacks/rack.c
index 98a6f0f2e924..f5b0de7cbc59 100644
--- a/sys/netinet/tcp_stacks/rack.c
+++ b/sys/netinet/tcp_stacks/rack.c
@@ -12297,7 +12297,8 @@ rack_output(struct tcpcb *tp)
 	 * If sack_rxmit is true we are retransmitting from the scoreboard
 	 * in which case len is already set.
 	 */
-	if ((sack_rxmit == 0) && TCPS_HAVEESTABLISHED(tp->t_state)) {
+	if ((sack_rxmit == 0) &&
+	    (TCPS_HAVEESTABLISHED(tp->t_state) || IS_FASTOPEN(tp->t_flags))) {
 		uint32_t avail;
 
 		avail = sbavail(sb);