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, 3 insertions, 3 deletions

diff --git a/sys/netinet6/in6.h b/sys/netinet6/in6.h
index 6ab33419335..5e51cbb17b8 100644
--- a/sys/netinet6/in6.h
+++ b/sys/netinet6/in6.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: in6.h,v 1.105 2019/11/11 17:42:29 bluhm Exp $	*/
+/*	$OpenBSD: in6.h,v 1.106 2020/06/24 22:03:44 cheloha Exp $	*/
 /*	$KAME: in6.h,v 1.83 2001/03/29 02:55:07 jinmei Exp $	*/
 
 /*
@@ -280,11 +280,11 @@ struct route_in6 {
 
 #define IFA6_IS_DEPRECATED(a) \
 	((a)->ia6_lifetime.ia6t_pltime != ND6_INFINITE_LIFETIME && \
-	 (u_int32_t)((time_uptime - (a)->ia6_updatetime)) > \
+	 (u_int32_t)((getuptime() - (a)->ia6_updatetime)) > \
 	 (a)->ia6_lifetime.ia6t_pltime)
 #define IFA6_IS_INVALID(a) \
 	((a)->ia6_lifetime.ia6t_vltime != ND6_INFINITE_LIFETIME && \
-	 (u_int32_t)((time_uptime - (a)->ia6_updatetime)) > \
+	 (u_int32_t)((getuptime() - (a)->ia6_updatetime)) > \
 	 (a)->ia6_lifetime.ia6t_vltime)
 
 #endif /* _KERNEL */