[tip:timers/urgent] clocksource: Consistent de-rate when marking unstable

[tip-bot for Peter Zijlstra <tipbot@zytor.com>]

Commit-ID:  cd2af07d823e5287cd6c91d54337348c2a873462
Gitweb:     https://git.kernel.org/tip/cd2af07d823e5287cd6c91d54337348c2a873462
Author:     Peter Zijlstra <peterz@infradead.org>
AuthorDate: Mon, 30 Apr 2018 12:00:13 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 2 May 2018 16:10:41 +0200

clocksource: Consistent de-rate when marking unstable

When a registered clocksource gets marked unstable the watchdog_kthread
will de-rate and re-select the clocksource. Ensure it also de-rates
when getting called on an unregistered clocksource.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: len.brown@intel.com
Cc: rjw@rjwysocki.net
Cc: diego.viola@gmail.com
Cc: rui.zhang@intel.com
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180430100344.594904898@infradead.org

---
 kernel/time/clocksource.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 935f39eb8aac..605656df16c4 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -152,12 +152,19 @@ static void __clocksource_unstable(struct clocksource *cs)
 	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
 	cs->flags |= CLOCK_SOURCE_UNSTABLE;
 
-	if (list_empty(&cs->list))
+	/*
+	 * If the clocksource is registered clocksource_watchdog_kthread() will
+	 * re-rate and re-select.
+	 */
+	if (list_empty(&cs->list)) {
+		cs->rating = 0;
 		return;
+	}
 
 	if (cs->mark_unstable)
 		cs->mark_unstable(cs);
 
+	/* kick clocksource_watchdog_kthread() */
 	if (finished_booting)
 		schedule_work(&watchdog_work);
 }