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Subject[PATCH] Clocksource: Avoid misjudgment of clocksource
Date
clocksource_watchdog is executed every WATCHDOG_INTERVAL(0.5s) by
Timer. But sometimes system is very busy and the Timer cannot be
executed in 0.5sec. For example,if clocksource_watchdog be executed
after 10sec, the calculated value of abs(cs_nsec - wd_nsec) will
be enlarged. Then the current clocksource will be misjudged as
unstable. So we add conditions to prevent the clocksource from
being misjudged.

Signed-off-by: yanghui <yanghui.def@bytedance.com>
---
kernel/time/clocksource.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index b8a14d2fb5ba..d535beadcbc8 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -136,8 +136,10 @@ static void __clocksource_change_rating(struct clocksource *cs, int rating);

/*
* Interval: 0.5sec.
+ * MaxInterval: 1s.
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
+#define WATCHDOG_MAX_INTERVAL_NS (NSEC_PER_SEC)

static void clocksource_watchdog_work(struct work_struct *work)
{
@@ -404,7 +406,9 @@ static void clocksource_watchdog(struct timer_list *unused)

/* Check the deviation from the watchdog clocksource. */
md = cs->uncertainty_margin + watchdog->uncertainty_margin;
- if (abs(cs_nsec - wd_nsec) > md) {
+ if ((abs(cs_nsec - wd_nsec) > md) &&
+ cs_nsec < WATCHDOG_MAX_INTERVAL_NS &&
+ wd_nsec < WATCHDOG_MAX_INTERVAL_NS) {
pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
smp_processor_id(), cs->name);
pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
--
2.20.1
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