| Re: [chrony-dev] makestep command sometimes makes chrony stop reading its sources |
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On Thu, 21 Jan 2010, Miroslav Lichvar wrote:
On Thu, Jan 21, 2010 at 03:00:19PM +0100, Hattink, Tjalling (FINT) wrote:
The freeze is probably worth investigating.
I've investigated it and it has actually nothing to do with makestep.
When I set the RTC clock 40 months back or forward in time, the chrony
daemon freezes as soon as it selects a reference clock. I think there is
an integer overflow somewhere.
Yes, I reproduced it too. The calculated timeout for ending fast slew
(which should be 40 / 0.08 months) overflows, the timestamp is
negative, the handler is immediately called which adds the timeout
again...
We can limit the timeout to something reasonable like one month or add
checks for signed overflows to UTI_ functions (which will possibly
have a performance impact).
How much do we care about year 2038?
2038 is coming and now is probably the time to start worrying.
Well, we certainly should make the seconds a time_t rather than long
(eg in UTI_DoubleTotimeval) even if time_t is defined as long now.
Also I agree that they are problematic in that the routines assume that the double is
less than 2 10^9 sec. which it need not be. (the usec would sure come out
pretty weirdly for larger numbers)
Where is that overflow occuring? Certainly the UTI functions should be good
for much more than 40 months (or is it that 40/.08 months from now is overflowing 2038?)
I suspect that chrony should not be trying to slew that huge a difference
from local time-- it should either throw an exception, or just step.
While the 1/8 second stepping of ntpd is silly, stepping 40 months rather than
slewing it for the next century sounds pretty reasonable. In fact anything
over a day or certainly a year sounds reasonable to step.
--
William G. Unruh | Canadian Institute for| Tel: +1(604)822-3273
Physics&Astronomy | Advanced Research | Fax: +1(604)822-5324
UBC, Vancouver,BC | Program in Cosmology | unruh@xxxxxxxxxxxxxx
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