From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: John Stultz To: Linux Kernel Cc: John Stultz , Prarit Bhargava , stable@vger.kernel.org, Thomas Gleixner Subject: [PATCH 0/3] Fix for leapsecond caused hrtimer/futex issue Date: Thu, 5 Jul 2012 15:12:15 -0400 Message-Id: <1341515538-5100-1-git-send-email-johnstul@us.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: Thomas: So Prarit and my testing over the last few days have gone fine, and its been quiet otherwise, so I wanted to go ahead and submit this for inclusion. As widely reported on the internet, many Linux systems after the leapsecond was inserted experienced 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 This issue stemmed from the timekeeping subsystem not notifying the hrtimer subsystem that the leapsecond occurred, causing CLOCK_REALTIME hritmers to be fired one second early, and sub-second CLOCK_REALTIME hrtimer timeouts to fire immediately (causing the load spikes). To address this issue I'm proposing we do three 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. 3) Change hrtimer_interrupt to update the hrtimer base offset values. This third item provides additional robustness should the clock_was_set() notification (done via a timer if we're in_atomic) be delayed significantly. 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). Please email lkml and me if you experienced this. Big thanks to Prarit for shaking out a few issues in the earlier version of this patch set, as well as the extra effort testing over the Holiday! Also, I've already got backports generated for -stable, that I'm testing and I'll submitting them once I have upstream commit ids for these patches. thanks -john CC: Prarit Bhargava CC: stable@vger.kernel.org CC: Thomas Gleixner John Stultz (3): hrtimer: Fix clock_was_set so it is safe to call from irq context time: Fix leapsecond triggered hrtimer/futex load spike issue hrtimer: Update hrtimer base offsets each hrtimer_interrupt include/linux/hrtimer.h | 3 +++ kernel/hrtimer.c | 31 +++++++++++++++++++++++++++---- kernel/time/timekeeping.c | 38 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 68 insertions(+), 4 deletions(-) -- 1.7.9.5