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Date:      Tue, 21 Apr 2020 13:05:44 +0000 (UTC)
From:      Richard Scheffenegger <rscheff@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r360143 - in head/sys/netinet: . tcp_stacks
Message-ID:  <202004211305.03LD5im9045434@repo.freebsd.org>
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Author: rscheff
Date: Tue Apr 21 13:05:44 2020
New Revision: 360143
URL: https://svnweb.freebsd.org/changeset/base/360143

Log:
  Correctly set up the initial TCP congestion window
  in all cases, by adjust snd_una right after the
  connection initialization, to include the one byte
  in sequence space occupied by the SYN bit.
  
  This does not change the regular ACK processing,
  while making the BYTES_THIS_ACK macro to work properly.
  
  PR:		235256
  Reviewed by:	tuexen (mentor), rgrimes (mentor)
  Approved by:	tuexen (mentor), rgrimes (mentor)
  MFC after:	2 weeks
  Sponsored by:	NetApp, Inc.
  Differential Revision:	https://reviews.freebsd.org/D19000

Modified:
  head/sys/netinet/tcp_input.c
  head/sys/netinet/tcp_stacks/bbr.c
  head/sys/netinet/tcp_stacks/rack.c

Modified: head/sys/netinet/tcp_input.c
==============================================================================
--- head/sys/netinet/tcp_input.c	Tue Apr 21 05:00:35 2020	(r360142)
+++ head/sys/netinet/tcp_input.c	Tue Apr 21 13:05:44 2020	(r360143)
@@ -2374,12 +2374,6 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
 		if (IS_FASTOPEN(tp->t_flags) && tp->t_tfo_pending) {
 			tcp_fastopen_decrement_counter(tp->t_tfo_pending);
 			tp->t_tfo_pending = NULL;
-
-			/*
-			 * Account for the ACK of our SYN prior to
-			 * regular ACK processing below.
-			 */
-			tp->snd_una++;
 		}
 		if (tp->t_flags & TF_NEEDFIN) {
 			tcp_state_change(tp, TCPS_FIN_WAIT_1);
@@ -2399,6 +2393,12 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
 				cc_conn_init(tp);
 			tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 		}
+		if (SEQ_GT(th->th_ack, tp->snd_una))
+			/*
+			 * Account for the ACK of our SYN prior to
+			 * regular ACK processing below.
+			 */
+			tp->snd_una++;
 		/*
 		 * If segment contains data or ACK, will call tcp_reass()
 		 * later; if not, do so now to pass queued data to user.

Modified: head/sys/netinet/tcp_stacks/bbr.c
==============================================================================
--- head/sys/netinet/tcp_stacks/bbr.c	Tue Apr 21 05:00:35 2020	(r360142)
+++ head/sys/netinet/tcp_stacks/bbr.c	Tue Apr 21 13:05:44 2020	(r360143)
@@ -9325,11 +9325,6 @@ bbr_do_syn_recv(struct mbuf *m, struct tcphdr *th, str
 
 		tcp_fastopen_decrement_counter(tp->t_tfo_pending);
 		tp->t_tfo_pending = NULL;
-		/*
-		 * Account for the ACK of our SYN prior to regular
-		 * ACK processing below.
-		 */
-		tp->snd_una++;
 	}
 	/*
 	 * Make transitions: SYN-RECEIVED  -> ESTABLISHED SYN-RECEIVED* ->
@@ -9352,6 +9347,12 @@ bbr_do_syn_recv(struct mbuf *m, struct tcphdr *th, str
 		if (!IS_FASTOPEN(tp->t_flags))
 			cc_conn_init(tp);
 	}
+	if (SEQ_GT(th->th_ack, tp->snd_una))
+		/*
+		 * Account for the ACK of our SYN prior to
+		 * regular ACK processing below.
+		 */
+		tp->snd_una++;
 	/*
 	 * If segment contains data or ACK, will call tcp_reass() later; if
 	 * not, do so now to pass queued data to user.

Modified: head/sys/netinet/tcp_stacks/rack.c
==============================================================================
--- head/sys/netinet/tcp_stacks/rack.c	Tue Apr 21 05:00:35 2020	(r360142)
+++ head/sys/netinet/tcp_stacks/rack.c	Tue Apr 21 13:05:44 2020	(r360143)
@@ -6539,12 +6539,6 @@ rack_do_syn_recv(struct mbuf *m, struct tcphdr *th, st
 	if (IS_FASTOPEN(tp->t_flags) && tp->t_tfo_pending) {
 		tcp_fastopen_decrement_counter(tp->t_tfo_pending);
 		tp->t_tfo_pending = NULL;
-
-		/*
-		 * Account for the ACK of our SYN prior to
-		 * regular ACK processing below.
-		 */
-		tp->snd_una++;
 	}
 	if (tp->t_flags & TF_NEEDFIN) {
 		tcp_state_change(tp, TCPS_FIN_WAIT_1);
@@ -6562,6 +6556,12 @@ rack_do_syn_recv(struct mbuf *m, struct tcphdr *th, st
 		if (!IS_FASTOPEN(tp->t_flags))
 			cc_conn_init(tp);
 	}
+	if (SEQ_GT(th->th_ack, tp->snd_una))
+		/*
+		 * Account for the ACK of our SYN prior to
+		 * regular ACK processing below.
+		 */
+		tp->snd_una++;
 	/*
 	 * If segment contains data or ACK, will call tcp_reass() later; if
 	 * not, do so now to pass queued data to user.

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