diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -1872,9 +1872,11 @@
 				 * is new data available to be sent
 				 * or we need to send an ACK.
 				 */
-				if (SEQ_GT(tp->snd_una + sbavail(&so->so_snd),
-				    tp->snd_max) || tp->t_flags & TF_ACKNOW)
+				if ((tp->t_flags & TF_ACKNOW) ||
+				    SEQ_GEQ(sbavail(&so->so_snd),
+				    SEQ_SUB(tp->snd_max, tp->snd_una))) {
 					(void) tcp_output(tp);
+				}
 				goto check_delack;
 			}
 		} else if (th->th_ack == tp->snd_una &&
@@ -2585,11 +2587,13 @@
 				 */
 				if (th->th_ack != tp->snd_una ||
 				    (tcp_is_sack_recovery(tp, &to) &&
-				    (sack_changed == SACK_NOCHANGE)))
+				    (sack_changed == SACK_NOCHANGE))) {
 					break;
-				else if (!tcp_timer_active(tp, TT_REXMT))
+				} else
+				if (!tcp_timer_active(tp, TT_REXMT)) {
 					tp->t_dupacks = 0;
-				else if (++tp->t_dupacks > tcprexmtthresh ||
+				} else
+				if (++tp->t_dupacks > tcprexmtthresh ||
 				     IN_FASTRECOVERY(tp->t_flags)) {
 					cc_ack_received(tp, th, nsegs,
 					    CC_DUPACK);
@@ -2597,7 +2601,8 @@
 					    IN_FASTRECOVERY(tp->t_flags) &&
 					    (tp->t_flags & TF_SACK_PERMIT)) {
 						tcp_do_prr_ack(tp, th, &to, sack_changed);
-					} else if (tcp_is_sack_recovery(tp, &to) &&
+					} else
+					if (tcp_is_sack_recovery(tp, &to) &&
 					    IN_FASTRECOVERY(tp->t_flags)) {
 						int awnd;
 
@@ -2607,26 +2612,28 @@
 						 * we have less than 1/2 the original window's
 						 * worth of data in flight.
 						 */
-						if (V_tcp_do_newsack)
+						if (V_tcp_do_newsack) {
 							awnd = tcp_compute_pipe(tp);
-						else
+						} else {
 							awnd = (tp->snd_nxt - tp->snd_fack) +
 								tp->sackhint.sack_bytes_rexmit;
-
+						}
 						if (awnd < tp->snd_ssthresh) {
 							tp->snd_cwnd += maxseg;
 							if (tp->snd_cwnd > tp->snd_ssthresh)
 								tp->snd_cwnd = tp->snd_ssthresh;
 						}
-					} else
+					} else {
 						tp->snd_cwnd += maxseg;
+					}
 					(void) tcp_output(tp);
 					goto drop;
-				} else if (tp->t_dupacks == tcprexmtthresh ||
-					    (tp->t_flags & TF_SACK_PERMIT &&
-					     V_tcp_do_newsack &&
-					     tp->sackhint.sacked_bytes >
-					     (tcprexmtthresh - 1) * maxseg)) {
+				} else
+				if (tp->t_dupacks == tcprexmtthresh ||
+				    (tp->t_flags & TF_SACK_PERMIT &&
+				     V_tcp_do_newsack &&
+				     tp->sackhint.sacked_bytes >
+				     (tcprexmtthresh - 1) * maxseg)) {
 enter_recovery:
 					/*
 					 * Above is the RFC6675 trigger condition of
@@ -2687,13 +2694,13 @@
 						    tp->snd_nxt - tp->snd_una);
 					}
 					if (tcp_is_sack_recovery(tp, &to)) {
-						TCPSTAT_INC(
-						    tcps_sack_recovery_episode);
+						TCPSTAT_INC(tcps_sack_recovery_episode);
 						tp->snd_recover = tp->snd_nxt;
 						tp->snd_cwnd = maxseg;
 						(void) tcp_output(tp);
-						if (SEQ_GT(th->th_ack, tp->snd_una))
+						if (SEQ_GT(th->th_ack, tp->snd_una)) {
 							goto resume_partialack;
+						}
 						goto drop;
 					}
 					tp->snd_nxt = th->th_ack;
@@ -2708,7 +2715,8 @@
 					if (SEQ_GT(onxt, tp->snd_nxt))
 						tp->snd_nxt = onxt;
 					goto drop;
-				} else if (V_tcp_do_rfc3042) {
+				} else
+				if (V_tcp_do_rfc3042) {
 					/*
 					 * Process first and second duplicate
 					 * ACKs. Each indicates a segment
@@ -2719,8 +2727,7 @@
 					 * segment. Restore the original
 					 * snd_cwnd after packet transmission.
 					 */
-					cc_ack_received(tp, th, nsegs,
-					    CC_DUPACK);
+					cc_ack_received(tp, th, nsegs, CC_DUPACK);
 					uint32_t oldcwnd = tp->snd_cwnd;
 					tcp_seq oldsndmax = tp->snd_max;
 					u_int sent;
@@ -2743,11 +2750,12 @@
 					 */
 					SOCKBUF_LOCK(&so->so_snd);
 					avail = sbavail(&so->so_snd) -
-					    (tp->snd_nxt - tp->snd_una);
+					    SEQ_SUB(tp->snd_nxt, tp->snd_una);
 					SOCKBUF_UNLOCK(&so->so_snd);
-					if (avail > 0 || tp->t_flags & TF_ACKNOW)
+					if (avail > 0 || tp->t_flags & TF_ACKNOW) {
 						(void) tcp_output(tp);
-					sent = tp->snd_max - oldsndmax;
+					}
+					sent = SEQ_SUB(tp->snd_max, oldsndmax);
 					if (sent > maxseg) {
 						KASSERT((tp->t_dupacks == 2 &&
 						    tp->snd_limited == 0) ||
@@ -2756,8 +2764,10 @@
 						    ("%s: sent too much",
 						    __func__));
 						tp->snd_limited = 2;
-					} else if (sent > 0)
+					} else
+					if (sent > 0) {
 						++tp->snd_limited;
+					}
 					tp->snd_cwnd = oldcwnd;
 					goto drop;
 				}
@@ -3308,9 +3318,9 @@
 	/*
 	 * Return any desired output.
 	 */
-	if (needoutput || (tp->t_flags & TF_ACKNOW))
+	if (needoutput || (tp->t_flags & TF_ACKNOW)) {
 		(void) tcp_output(tp);
-
+	}
 check_delack:
 	INP_WLOCK_ASSERT(inp);
 
@@ -4020,8 +4030,10 @@
 			tp->snd_cwnd = (tp->snd_max - tp->snd_una) +
 					    (snd_cnt * maxseg);
 		}
-	} else if (IN_CONGRECOVERY(tp->t_flags))
+	} else
+	if (IN_CONGRECOVERY(tp->t_flags)) {
 		tp->snd_cwnd = pipe - del_data + (snd_cnt * maxseg);
+	}
 	tp->snd_cwnd = imax(maxseg, tp->snd_cwnd);
 }
 
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -395,10 +395,10 @@
 	 * in which case len is already set.
 	 */
 	if (sack_rxmit == 0) {
-		if (sack_bytes_rxmt == 0)
+		if (sack_bytes_rxmt == 0) {
 			len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
 			    off);
-		else {
+		} else {
 			int32_t cwin;
 
 			/*
@@ -561,12 +561,8 @@
 	    ipoptlen == 0 && !(flags & TH_SYN))
 		tso = 1;
 
-	if (sack_rxmit) {
-		if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
-			flags &= ~TH_FIN;
-	} else {
-		if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
-		    sbused(&so->so_snd)))
+	if (SEQ_LT((sack_rxmit ? p->rxmit : tp->snd_nxt) + len,
+		    tp->snd_una + sbused(&so->so_snd))) {
 			flags &= ~TH_FIN;
 	}
 
@@ -612,9 +608,8 @@
 		if (!(tp->t_flags & TF_MORETOCOME) &&	/* normal case */
 		    (idle || (tp->t_flags & TF_NODELAY)) &&
 		    (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
-		    (tp->t_flags & TF_NOPUSH) == 0) {
+		    (tp->t_flags & TF_NOPUSH) == 0)
 			goto send;
-		}
 		if (tp->t_flags & TF_FORCEDATA)		/* typ. timeout case */
 			goto send;
 		if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
diff --git a/sys/netinet/tcp_sack.c b/sys/netinet/tcp_sack.c
--- a/sys/netinet/tcp_sack.c
+++ b/sys/netinet/tcp_sack.c
@@ -983,12 +983,13 @@
 		if (tp->t_flags & TF_SENTFIN)
 			highdata--;
 		highdata = SEQ_MIN(highdata, tp->snd_recover);
-		if (th->th_ack != highdata) {
+		if (SEQ_LT(th->th_ack, highdata)) {
 			tp->snd_fack = th->th_ack;
 			if ((temp = tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
-			    highdata - maxseg), highdata, NULL)) != NULL)
-				tp->sackhint.hole_bytes += temp->end -
-								temp->start;
+			    highdata - maxseg), highdata, NULL)) != NULL) {
+				tp->sackhint.hole_bytes +=
+					temp->end - temp->start;
+			}
 		}
 	}
 	(void) tcp_output(tp);
@@ -1060,27 +1061,33 @@
 	struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
 
 	INP_WLOCK_ASSERT(tptoinpcb(tp));
-	if (cur == NULL)
-		return; /* No holes */
-	if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
-		return; /* We're already beyond any SACKed blocks */
+	if (cur == NULL) {
+		/* No holes */
+		return;
+	}
+	if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack)) {
+		/* We're already beyond any SACKed blocks */
+		return;
+	}
 	/*-
 	 * Two cases for which we want to advance snd_nxt:
 	 * i) snd_nxt lies between end of one hole and beginning of another
 	 * ii) snd_nxt lies between end of last hole and snd_fack
 	 */
 	while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
-		if (SEQ_LT(tp->snd_nxt, cur->end))
+		if (SEQ_LT(tp->snd_nxt, cur->end)) {
 			return;
-		if (SEQ_GEQ(tp->snd_nxt, p->start))
+		}
+		if (SEQ_GEQ(tp->snd_nxt, p->start)) {
 			cur = p;
-		else {
+		} else {
 			tp->snd_nxt = p->start;
 			return;
 		}
 	}
-	if (SEQ_LT(tp->snd_nxt, cur->end))
+	if (SEQ_LT(tp->snd_nxt, cur->end)) {
 		return;
+	}
 	tp->snd_nxt = tp->snd_fack;
 }