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    SubjectRe: Leap second insertion causes futex to repeatedly timeout
    On 07/01/2012 01:36 AM, Ben Blum wrote:
    > On Sun, Jul 01, 2012 at 01:16:13AM -0700, john stultz wrote:
    >> On Sat, Jun 30, 2012 at 5:57 PM, Jan Engelhardt <> 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 - - 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:
    > In short, clock_was_set() calls on_each_cpu() which is not allowed to be
    > called in atomic context. Watch out for xtime_lock.

    Quite right. The fix is a little awkward due to the need to call it
    outside of holding xtime_lock/timekeeper.lock.

    I've just reproduced the issue w/ Thunderbird, and my fix seems to avoid
    the issue. Working up a patch now.


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