Messages in this thread | | | From | John Stultz <> | Subject | [PATCH 0/2][RFC] Potential fix for leapsecond caused futex issue (v2) | Date | Sun, 1 Jul 2012 14:29:59 -0400 |
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From: John Stultz <john.stultz@linaro.org>
Here's round two on this one.
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 workaround for this issue is running: $ date -s "`date`"
Credit: http://www.sheeri.com/content/mysql-and-leap-second-high-cpu-and-fix
To address this issue we do two things: 1) Fix the clock_was_set() call to remove the limitation that kept us from calling it from update_wall_time().
2) Call clock_was_set() when we add/remove a leapsecond.
I've been able to reproduce the load spike using Thunderbird when triggering a leap second and with this patch the issue did not crop up.
NOTE: Some reports have been of a hard hang right at or before the leapsecond. I've not been able to reproduce or diagnose this, so this fix does not likely address the reported hard hangs (unless they end up being connected to the futex/hrtimer issue).
TODOs: * Chase down the futex/hrtimer interaction to see if this could be triggered in any other way. * Get Tglx's input/ack * Generate a backport for pre-v3.4 kernels
v2: * Address the issue w/ calling clock_was_set from atomic context, pointed out by Prarit and Ben. * Rework fix so its simpler.
CC: Prarit Bhargava <prarit@redhat.com> CC: stable@vger.kernel.org CC: Thomas Gleixner <tglx@linutronix.de> Reported-by: Jan Engelhardt <jengelh@inai.de> Signed-off-by: John Stultz <johnstul@us.ibm.com>
John Stultz (2): [RFC] Fix clock_was_set so it is safe to call from atomic [RFC] Fix leapsecond triggered hrtimer/futex load spike issue
kernel/hrtimer.c | 16 +++++++++++++++- kernel/time/timekeeping.c | 4 ++++ 2 files changed, 19 insertions(+), 1 deletion(-)
-- 1.7.9.5
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