From a701e5dfafb22455e8cfbca0e7f2f834808b1a9d Mon Sep 17 00:00:00 2001
From: bluhm <bluhm@openbsd.org>
Date: Tue, 18 Sep 2018 20:47:11 +0000
Subject: [PATCH] Updating time counters without memory barriers is wrong.  Put
 membar_producer() into tc_windup() and membar_consumer() into the uptime
 functions.  They order the visibility of the time and generation number
 updates. This is a combination of what NetBSD and FreeBSD do. OK kettenis@

---
 sys/kern/kern_tc.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
index 9aa44703ac4..3d02cf70224 100644
--- a/sys/kern/kern_tc.c
+++ b/sys/kern/kern_tc.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_tc.c,v 1.33 2018/05/28 18:05:42 guenther Exp $ */
+/*	$OpenBSD: kern_tc.c,v 1.34 2018/09/18 20:47:11 bluhm Exp $ */
 
 /*
  * Copyright (c) 2000 Poul-Henning Kamp <phk@FreeBSD.org>
@@ -22,6 +22,7 @@
  */
 
 #include <sys/param.h>
+#include <sys/atomic.h>
 #include <sys/kernel.h>
 #include <sys/timeout.h>
 #include <sys/sysctl.h>
@@ -141,8 +142,10 @@ binuptime(struct bintime *bt)
 	do {
 		th = timehands;
 		gen = th->th_generation;
+		membar_consumer();
 		*bt = th->th_offset;
 		bintime_addx(bt, th->th_scale * tc_delta(th));
+		membar_consumer();
 	} while (gen == 0 || gen != th->th_generation);
 }
 
@@ -199,7 +202,9 @@ getnanouptime(struct timespec *tsp)
 	do {
 		th = timehands;
 		gen = th->th_generation;
+		membar_consumer();
 		bintime2timespec(&th->th_offset, tsp);
+		membar_consumer();
 	} while (gen == 0 || gen != th->th_generation);
 }
 
@@ -212,7 +217,9 @@ getmicrouptime(struct timeval *tvp)
 	do {
 		th = timehands;
 		gen = th->th_generation;
+		membar_consumer();
 		bintime2timeval(&th->th_offset, tvp);
+		membar_consumer();
 	} while (gen == 0 || gen != th->th_generation);
 }
 
@@ -225,7 +232,9 @@ getnanotime(struct timespec *tsp)
 	do {
 		th = timehands;
 		gen = th->th_generation;
+		membar_consumer();
 		*tsp = th->th_nanotime;
+		membar_consumer();
 	} while (gen == 0 || gen != th->th_generation);
 }
 
@@ -238,7 +247,9 @@ getmicrotime(struct timeval *tvp)
 	do {
 		th = timehands;
 		gen = th->th_generation;
+		membar_consumer();
 		*tvp = th->th_microtime;
+		membar_consumer();
 	} while (gen == 0 || gen != th->th_generation);
 }
 
@@ -390,6 +401,7 @@ tc_windup(void)
 	th = tho->th_next;
 	ogen = th->th_generation;
 	th->th_generation = 0;
+	membar_producer();
 	memcpy(th, tho, offsetof(struct timehands, th_generation));
 
 	/*
@@ -481,11 +493,13 @@ tc_windup(void)
 	 */
 	if (++ogen == 0)
 		ogen = 1;
+	membar_producer();
 	th->th_generation = ogen;
 
 	/* Go live with the new struct timehands. */
 	time_second = th->th_microtime.tv_sec;
 	time_uptime = th->th_offset.sec;
+	membar_producer();
 	timehands = th;
 }
 
-- 
2.20.1