On Mon, May 05, 2014 at 08:49:01PM +0200, Stanislav Brabec wrote:
> Algorithm of calculation of hwclock adjustment is vulnerable to
> miscalculations. These miscalculations may lead to clock drifting by
> many years even after fixing CMOS hwclock failure.
>
> Following two patches are attempts to solve the most visible parts of
> the problem:
> - Calculation of excessive drift values in /etc/adjtime
> - Applying of excessive drift that causes many years clock failure.
> - It also prevents hangs before 4a44a54b.
Applied, thanks.
> There are further poor places in the code that are above the scope of
> this patch set:
> - Algorithm for detecting of invalid hwclock is very poor (valid_p fails
> only if hwclock output fails to pass mktime()).
> - There is no or failing discrimination between fine time adjustment and
> clock set.
> - In particular, proposed patch does not cover miscalculation while
> changing clock due to DST change, and more than 2 days passed since
> last adjustment. This could be covered by lowering of MAX_DRIFT, but
> heuristics for discrimination between adjustment and clock setting
> would be much better.
> - Most of failures fixed by these patches were hidden by a poor
> calculation of time passed since last adjustment:
> if ((hclocktime - adjtime_p->last_calib_time) < 23 * 60 * 60)
> (As there is no abs(), all times in past were considered as "less than
> one day ago".)
Look forward to see another patches ;-)
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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