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timekeeping: Fix leapsecond triggered load spike issue

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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@us.ibm.com>
Reported-by: Jan Engelhardt <jengelh@inai.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Cc: stable@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@linutronix.de>
This commit is contained in:
John Stultz 2012-07-10 18:43:20 -04:00 • committed by Thomas Gleixner
commit 4873fa070a
1 changed files with 4 additions and 0 deletions
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4
kernel/time/timekeeping.c
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@ -963,6 +963,8 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
leap = second_overflow(timekeeper.xtime.tv_sec); leap = second_overflow(timekeeper.xtime.tv_sec);
timekeeper.xtime.tv_sec += leap; timekeeper.xtime.tv_sec += leap;
timekeeper.wall_to_monotonic.tv_sec -= leap; timekeeper.wall_to_monotonic.tv_sec -= leap;
if (leap)
clock_was_set_delayed();
} }
/* Accumulate raw time */ /* Accumulate raw time */
@ -1079,6 +1081,8 @@ static void update_wall_time(void)
leap = second_overflow(timekeeper.xtime.tv_sec); leap = second_overflow(timekeeper.xtime.tv_sec);
timekeeper.xtime.tv_sec += leap; timekeeper.xtime.tv_sec += leap;
timekeeper.wall_to_monotonic.tv_sec -= leap; timekeeper.wall_to_monotonic.tv_sec -= leap;
if (leap)
clock_was_set_delayed();
} }
timekeeping_update(false); timekeeping_update(false);