From d25a025201ed98f4b93775e0999a3f2135702106 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Aug 2021 09:31:28 -0700 Subject: [PATCH] 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 Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/lkml/20210812000133.GA402890@paulmck-ThinkPad-P17-Gen-1/ --- kernel/time/clocksource-wdtest.c | 5 ++--- kernel/time/jiffies.c | 21 +-------------------- kernel/time/tick-internal.h | 20 ++++++++++++++++++++ 3 files changed, 23 insertions(+), 23 deletions(-) diff --git a/kernel/time/clocksource-wdtest.c b/kernel/time/clocksource-wdtest.c index 01df12395c0e..df922f49d171 100644 --- a/kernel/time/clocksource-wdtest.c +++ b/kernel/time/clocksource-wdtest.c @@ -19,6 +19,8 @@ #include #include +#include "tick-internal.h" + MODULE_LICENSE("GPL"); MODULE_AUTHOR("Paul E. McKenney "); @@ -34,9 +36,6 @@ static u64 wdtest_jiffies_read(struct clocksource *cs) return (u64)jiffies; } -/* Assume HZ > 100. */ -#define JIFFIES_SHIFT 8 - static struct clocksource clocksource_wdtest_jiffies = { .name = "wdtest-jiffies", .rating = 1, /* lowest valid rating*/ 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 #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; diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h index 3548f0829e6d..649f2b48e8f0 100644 --- a/kernel/time/tick-internal.h +++ b/kernel/time/tick-internal.h @@ -177,3 +177,23 @@ void clock_was_set(unsigned int bases); void clock_was_set_delayed(void); void hrtimers_resume_local(void); + +/* 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 -- 2.20.1