[PATCH 2/3] [QUANTAL] (pre-upstream) time: Fix leapsecond triggered hrtimer/futex load spike issue

[Brad Figg]

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

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

As widely reported on the internet, some Linux systems after
the leapsecond was inserted are experiencing futex related load
spikes (usually connected to MySQL, Firefox, Thunderbird, Java, etc).

An apparent for this issue workaround is running:
$ date -s "`date`"

Credit: http://www.sheeri.com/content/mysql-and-leap-second-high-cpu-and-fix

I this issue is due to the leapsecond being added without
calling clock_was_set() to notify the hrtimer subsystem of the
change.

The workaround functions as it forces a clock_was_set()
call from settimeofday().

This fix adds the required clock_was_set() calls to where
we adjust for leapseconds.

NOTE: This fix *depends* on the previous fix, which allows
clock_was_set to be called from atomic context. Do not try
to apply just this patch.

CC: Prarit Bhargava <prarit at redhat.com>
CC: stable at vger.kernel.org
CC: Thomas Gleixner <tglx at linutronix.de>
CC: linux at openhuawei.org
Reported-by: Jan Engelhardt <jengelh at inai.de>
Signed-off-by: John Stultz <johnstul at us.ibm.com>
Signed-off-by: Brad Figg <brad.figg at canonical.com>
---
 kernel/time/timekeeping.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 6f46a00..cc2991d 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -963,6 +963,8 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
 		leap = second_overflow(timekeeper.xtime.tv_sec);
 		timekeeper.xtime.tv_sec += leap;
 		timekeeper.wall_to_monotonic.tv_sec -= leap;
+		if (leap)
+			clock_was_set();
 	}
 
 	/* Accumulate raw time */
@@ -1079,6 +1081,8 @@ static void update_wall_time(void)
 		leap = second_overflow(timekeeper.xtime.tv_sec);
 		timekeeper.xtime.tv_sec += leap;
 		timekeeper.wall_to_monotonic.tv_sec -= leap;
+		if (leap)
+			clock_was_set();
 	}
 
 	timekeeping_update(false);
-- 
1.7.9.5