linux-kernel - [PATCH 2/3] [RFC] time: Fix leapsecond triggered hrtimer/futex load spike issue

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Message-Id: <1341382890-42324-3-git-send-email-johnstul@us.ibm.com>
Date:	Wed,  4 Jul 2012 02:21:29 -0400
From:	John Stultz <johnstul@...ibm.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>
Cc:	John Stultz <johnstul@...ibm.com>,
	Prarit Bhargava <prarit@...hat.com>, stable@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>, linux@...nhuawei.org
Subject: [PATCH 2/3] [RFC] time: Fix leapsecond triggered hrtimer/futex load spike issue

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@...hat.com>
CC: stable@...r.kernel.org
CC: Thomas Gleixner <tglx@...utronix.de>
CC: linux@...nhuawei.org
Reported-by: Jan Engelhardt <jengelh@...i.de>
Signed-off-by: John Stultz <johnstul@...ibm.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

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