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, 1 insertions, 1 deletions

diff --git a/sys/dev/pci/drm/include/linux/timekeeping.h b/sys/dev/pci/drm/include/linux/timekeeping.h
index c6aa77583c7..cd596d2e9ec 100644
--- a/sys/dev/pci/drm/include/linux/timekeeping.h
+++ b/sys/dev/pci/drm/include/linux/timekeeping.h
@@ -3,7 +3,7 @@
 #ifndef _LINUX_TIMEKEEPING_H
 #define _LINUX_TIMEKEEPING_H
 
-#define get_seconds()		time_second
+#define get_seconds()		gettime()
 #define getrawmonotonic(x)	nanouptime(x)
 
 #define ktime_mono_to_real(x) (x)