kernel: use gettime(9)/getuptime(9) in lieu of time_second(9)/time_uptime(9)

time_second(9) and time_uptime(9) are widely used in the kernel to
quickly get the system UTC or system uptime as a time_t.  However,
time_t is 64-bit everywhere, so it is not generally safe to use them
on 32-bit platforms: you have a split-read problem if your hardware
cannot perform atomic 64-bit reads.

This patch replaces time_second(9) with gettime(9), a safer successor
interface, throughout the kernel.  Similarly, time_uptime(9) is replaced
with getuptime(9).

There is a performance cost on 32-bit platforms in exchange for
eliminating the split-read problem: instead of two register reads you
now have a lockless read loop to pull the values from the timehands.
This is really not *too* bad in the grand scheme of things, but
compared to what we were doing before it is several times slower.

There is no performance cost on 64-bit (__LP64__) platforms.

With input from visa@, dlg@, and tedu@.

Several bugs squashed by visa@.

ok kettenis@

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/arch/loongson/dev/apm.c b/sys/arch/loongson/dev/apm.c
index 42b3d7c61ba..250d69d248e 100644
--- a/sys/arch/loongson/dev/apm.c
+++ b/sys/arch/loongson/dev/apm.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: apm.c,v 1.37 2020/05/29 04:42:24 deraadt Exp $	*/
+/*	$OpenBSD: apm.c,v 1.38 2020/06/24 22:03:40 cheloha Exp $	*/
 
 /*-
  * Copyright (c) 2001 Alexander Guy.  All rights reserved.
@@ -415,7 +415,7 @@ apm_suspend(int state)
 		if (rv == 0)
 			rv = sys_platform->resume();
 	}
-	inittodr(time_second);	/* Move the clock forward */
+	inittodr(gettime());	/* Move the clock forward */
 	config_suspend_all(DVACT_RESUME);
 
 	cold = 0;