[PATCH 06/11] 2.6.32.x: timekeeping: Fix leapsecond triggered load spike issue

[Luis Henriques]

From: John Stultz <johnstul at us.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1020285

This is a backport of 4873fa070ae84a4115f0b3c9dfabc224f1bc7c51

The timekeeping code misses an update of the hrtimer subsystem after a
leap second happened. Due to that timers based on CLOCK_REALTIME are
either expiring a second early or late depending on whether a leap
second has been inserted or deleted until an operation is initiated
which causes that update. Unless the update happens by some other
means this discrepancy between the timekeeping and the hrtimer data
stays forever and timers are expired either early or late.

The reported immediate workaround - $ data -s "`date`" - is causing a
call to clock_was_set() which updates the hrtimer data structures.
See: http://www.sheeri.com/content/mysql-and-leap-second-high-cpu-and-fix

Add the missing clock_was_set() call to update_wall_time() in case of
a leap second event. The actual update is deferred to softirq context
as the necessary smp function call cannot be invoked from hard
interrupt context.

Signed-off-by: John Stultz <johnstul at us.ibm.com>
Reported-by: Jan Engelhardt <jengelh at inai.de>
Reviewed-by: Ingo Molnar <mingo at kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra at chello.nl>
Acked-by: Prarit Bhargava <prarit at redhat.com>
Cc: stable at vger.kernel.org
Link: http://lkml.kernel.org/r/1341960205-56738-3-git-send-email-johnstul@us.ibm.com
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: Prarit Bhargava <prarit at redhat.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Linux Kernel <linux-kernel at vger.kernel.org>
Signed-off-by: John Stultz <johnstul at us.ibm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/time/timekeeping.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index a969adf..1e9808d 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -790,6 +790,8 @@ void update_wall_time(void)
 			leap = second_overflow(xtime.tv_sec);
 			xtime.tv_sec += leap;
 			wall_to_monotonic.tv_sec -= leap;
+			if (leap)
+				clock_was_set_delayed();
 		}
 
 		raw_time.tv_nsec += timekeeper.raw_interval;
-- 
1.7.9.5