hwclock can cause system lockup

[Chris]

2008/10/17 Todd Denniston <Todd.Denniston at ssa.crane.navy.mil>

> Mikkel L. Ellertson wrote, On 10/16/2008 05:23 PM:
>>
>> What are you trying to do with this cron job? You are updating the
>> system clock from the hardware clock, and not the other way around,
>> as you say you are trying to do. The system does synchronize the
>> hardware clock to the system clock on shutdown.
>>
>
> Not if you are sane enough to disable that in the halt script.
> (search this or the fedora-test list for ntp and me to see why I say this)I
> would suggest two things:


Strangely I can't find anything, I googled "ntp denniston site:
www.redhat.com/archives/fedora-list/" and the same for fedora-test-list but
no results were found.

1) see if punching the calls up to .5Hz or 1Hz instead of .3Hz gets it
>

Pretty much the same behaviour, it runs for a period of time before the
system locks up. The idea of running it every 3 seconds was simply to
accelerate my investigations. Normally it would run once per hour and the
lockup would occur anything from once per day to once in a couple of weeks.
Fortunately I have quite a few test machines I can use. They all do it, some
more than others. There are maybe 3 or 4 different motherboards in use from
different manufacturers so I'd be surprised if it's a problem specific to a
certain clock chip (but by coincidence they may have the same one).


> 2) booting in runlevel 3 and running the script again and see if it gets
> you the error in a few hours, hopefully this time with an OOPS or Panic
> message.


I did this but I didn't see any kernel messages, just the locked up screen.
It only took 30-45 minutes when running at 1 second intervals.

If any of these ends up being again 'just over an hour before it locked up'
> it might be some interaction with another cron job... did you disable the
> hourly cron job first?  if not I would set your 3 second script and a 2
> minute cron and see if it may be a '2 accesses at the same time' problem.
>

In all these tests I did disable the cron job. I can't see anything else
that could be interacting, only the normal system services are running.
There are a few of the standard daily cron jobs enabled but the system fails
at times when none of these jobs are running so I'm confident they can be
ruled out.


> race conditions in time, oh what fun.
>

Oh yes, I'm having the time of my life. :) Thanks for the suggestions.
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