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    SubjectRe: Leap second insertion causes futex to repeatedly timeout
    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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