clocksource: Make clocksource watchdog test safe for slow-HZ systems

The clocksource watchdog test sets a local JIFFIES_SHIFT macro and assumes
that HZ is >= 100. For smaller HZ values this shift value is too large and
causes undefined behaviour.

Move the HZ-based definitions of JIFFIES_SHIFT from kernel/time/jiffies.c
to kernel/time/tick-internal.h so the clocksource watchdog test can utilize
them, which makes it work correctly with all HZ values.

[ tglx: Resolved conflicts and massaged changelog ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/20210812000133.GA402890@paulmck-ThinkPad-P17-Gen-1/

1 files changed, 1 insertions, 20 deletions

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index 01935aafdb46..bc4db9e5ab70 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -10,28 +10,9 @@
 #include <linux/init.h>
 
 #include "timekeeping.h"
+#include "tick-internal.h"
 
 
-/* Since jiffies uses a simple TICK_NSEC multiplier
- * conversion, the .shift value could be zero. However
- * this would make NTP adjustments impossible as they are
- * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
- * shift both the nominator and denominator the same
- * amount, and give ntp adjustments in units of 1/2^8
- *
- * The value 8 is somewhat carefully chosen, as anything
- * larger can result in overflows. TICK_NSEC grows as HZ
- * shrinks, so values greater than 8 overflow 32bits when
- * HZ=100.
- */
-#if HZ < 34
-#define JIFFIES_SHIFT	6
-#elif HZ < 67
-#define JIFFIES_SHIFT	7
-#else
-#define JIFFIES_SHIFT	8
-#endif
-
 static u64 jiffies_read(struct clocksource *cs)
 {
 	return (u64) jiffies;