Re: Leap second insertion causes futex to repeatedly timeout
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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 <jengelh@xxxxxxx> 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@xxxxxxxxxxxxxxx/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.
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.
thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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