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authorPaul E. McKenney <paulmck@kernel.org>2021-08-12 19:31:28 +0300
committerThomas Gleixner <tglx@linutronix.de>2021-08-28 18:01:32 +0300
commitd25a025201ed98f4b93775e0999a3f2135702106 (patch)
tree2fcc4adf70cf9f897619f188db2dc97392667139 /kernel
parent127c92feb74a6721f62587f1b89128808f049cf1 (diff)
downloadlinux-d25a025201ed98f4b93775e0999a3f2135702106.tar.xz
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/
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/clocksource-wdtest.c5
-rw-r--r--kernel/time/jiffies.c21
-rw-r--r--kernel/time/tick-internal.h20
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 <linux/prandom.h>
#include <linux/cpu.h>
+#include "tick-internal.h"
+
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Paul E. McKenney <paulmck@kernel.org>");
@@ -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 <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;
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