[GIT pull] time(r) fixes for 5.6-rc1

[Thomas Gleixner]

Linus,

please pull the latest timers/urgent branch from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers-urgent-2020-02-09

up to:  febac332a819: clocksource: Prevent double add_timer_on() for watchdog_timer


Two small fixes for the time(r) subsystem:

  - Handle a subtle race between the clocksource watchdog and a concurrent
    clocksource watchdog stop/start sequence correctly to prevent a timer
    double add bug.

  - Fix the file path for the core time namespace file.


Thanks,

	tglx

------------------>
Dmitry Safonov (1):
      MAINTAINERS: Correct path to time namespace source file

Konstantin Khlebnikov (1):
      clocksource: Prevent double add_timer_on() for watchdog_timer


 MAINTAINERS               |  2 +-
 kernel/time/clocksource.c | 11 +++++++++--
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index 141b8d3e4ca2..3a4163be98da 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13267,7 +13267,7 @@ S:	Maintained
 F:	fs/timerfd.c
 F:	include/linux/timer*
 F:	include/linux/time_namespace.h
-F:	kernel/time_namespace.c
+F:	kernel/time/namespace.c
 F:	kernel/time/*timer*
 
 POWER MANAGEMENT CORE
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index fff5f64981c6..428beb69426a 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -293,8 +293,15 @@ static void clocksource_watchdog(struct timer_list *unused)
 	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
 	if (next_cpu >= nr_cpu_ids)
 		next_cpu = cpumask_first(cpu_online_mask);
-	watchdog_timer.expires += WATCHDOG_INTERVAL;
-	add_timer_on(&watchdog_timer, next_cpu);
+
+	/*
+	 * Arm timer if not already pending: could race with concurrent
+	 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
+	 */
+	if (!timer_pending(&watchdog_timer)) {
+		watchdog_timer.expires += WATCHDOG_INTERVAL;
+		add_timer_on(&watchdog_timer, next_cpu);
+	}
 out:
 	spin_unlock(&watchdog_lock);
 }