[chrony-dev] Chrony stuck in an endless loop

["Hattink, Tjalling [FINT]" <T.Hattink@xxxxxxxx>]

Hi,

Recently I've encountered a lockup of chrony on one of our embedded
boards running Linux. It was consuming all CPU resources and not acting
on any inputs anymore. I was able to attach a gdb debugger to the
process with symbols, so I could see the callstack and where it was
stuck.

The version I was using is 1.24. And it got stuck in the file regress.c,
line 570 to 578. The while loop there never exited. I also checked the
latest regress.c version in git, and I see the same loop at line 600 to
608, so I suspect the latest chrony is still affected by this issue.

The reason for getting stuck was that the blo and bhi variables never
changed. They both contained the same value -1.9333333333334166e-06. The
incr variable contained the value 9.061309612524684e-25. The reason why
blo and bhi didn't change was that incr is so small that it is
insignificant when added/substracted to blo and bhi.

After I changed the incr value to a much bigger number 1.0e-15 using gdb
the loop exited and chrony was working properly again.

The solution is to make sure incr contains a significant value before
going into the loop 570-578. Although I can't think of a good trick yet
to achieve this.

What are your thoughts about this? How should we fix this?

With best regards,

Tjalling Hattink

--
To unsubscribe email chrony-dev-request@xxxxxxxxxxxxxxxxxxxx with "unsubscribe" in the subject.
For help email chrony-dev-request@xxxxxxxxxxxxxxxxxxxx with "help" in the subject.
Trouble?  Email listmaster@xxxxxxxxxxxxxxxxxxxx.