timekeeping: Fix CLOCK_MONOTONIC inconsistency during leapsecond

This is a backport of fad0c66c
which resolves a bug the previous commit.

Commit 6b43ae8a (ntp: Fix leap-second hrtimer livelock) broke the
leapsecond update of CLOCK_MONOTONIC. The missing leapsecond update to
wall_to_monotonic causes discontinuities in CLOCK_MONOTONIC.

Adjust wall_to_monotonic when NTP inserted a leapsecond.
Reported-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Tested-by: Richard Cochran <richardcochran@gmail.com>
Link: http://lkml.kernel.org/r/1338400497-12420-1-git-send-email-john.stultz@linaro.orgSigned-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

kernel/time/timekeeping.c

@@ -938,6 +938,7 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
 		xtime.tv_sec++;
 		leap = second_overflow(xtime.tv_sec);
 		xtime.tv_sec += leap;
+		wall_to_monotonic.tv_sec -= leap;
 	}
 
 	/* Accumulate raw time */
@@ -1048,7 +1049,7 @@ static void update_wall_time(void)
 		xtime.tv_sec++;
 		leap = second_overflow(xtime.tv_sec);
 		xtime.tv_sec += leap;
-
+		wall_to_monotonic.tv_sec -= leap;
 	}
 
 	/* check to see if there is a new clocksource to use */