Messages in this thread | | | Date | Sun, 1 Jul 2012 04:36:05 -0400 | From | Ben Blum <> | Subject | Re: Leap second insertion causes futex to repeatedly timeout |
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On Sun, Jul 01, 2012 at 01:16:13AM -0700, john stultz wrote: > On Sat, Jun 30, 2012 at 5:57 PM, Jan Engelhardt <jengelh@inai.de> wrote: > > > > This year's leap second insertion has had the strange effect on at least > > Linux versions 3.4.4 (my end) and 3.5-rc4 (Simon's box, Cc) that certain > > processes use up all CPU power, because of futexes repeatedly timing > > out. This seems to only affect certain processes. > > > > Simon observes - http://s85.org/owXfmLvt - that > > Firefox/Thunderbird/Chrome/Java are affected. > > > > As for me, it affects VirtualBox, mysqld and ksoftirqd. The processes > > continue to run and respond. Most weird: I can stop-start mysqld and the > > issue persists. (I would have expected it to go away because the leap > > second event would then be in the past that mysqld does not know about > > anymore.) > > > > > > Is this a kernel issue? glibc? > > Some of the reports that the issue is resolved by calling: > $ date -s "`date`" > suggests that it might be due to clock_was_set() not being called > after the leap second was added, causing some hrtimer confusion. > > Thomas: does that sound about right? > > I've got an initial patch to add the clock_was_set() calls where > needed, but so far have not been able to reproduce the issue (tried > firefox and some simpler futex tests). I'll keep trying and hopefully > have something to send out tomorrow. > > Again, my apologies for the trouble.
I can't vouch for whether this is the problem or not, but be very careful with clock_was_set()! See this commit:
http://www.mail-archive.com/git-commits-head@vger.kernel.org/msg15039.html
In short, clock_was_set() calls on_each_cpu() which is not allowed to be called in atomic context. Watch out for xtime_lock.
Ben
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