Re: (ITS#8623) test022-ppolicy can fail due to timing dependency between lockout and expiration tests

[subbarao@computer.org]

On 03/22/2017 04:00 PM, Kartik Subbarao wrote:
> On 03/22/2017 03:11 PM, Howard Chu wrote:
>>> A recent 2.4.44 package build failed on a VM due to the following 
>>> timing
>>> dependency between the lockout and expiration tests in test022-ppolicy.
>>
>> Clocks on VMs are notoriously unstable, which is why we have always 
>> used such large margins in these tests. Shaving things down to "1 
>> second more than needed" will probably break in multiple build 
>> environments.
>
> Just to make sure we're understanding each other clearly -- are you 
> saying that you've seen VMs where "sleep 10" won't sleep for at 
> *least* 10 actual seconds? I haven't come across this, [...]

Hmm, the more I think about this, the harder it is for me to envision 
the kind of failure scenario you seem to be implying. Let me spell out 
my thought process and you can point out where I'm going wrong:

Assumption: An "unstable" clock on a VM is one that doesn't advance at 
one second per second of real-world time, but at least monotonically 
increases over time (ignoring DST exceptions and rare things like that). 
If it's *not* monotonically increasing, then I don't see how all kinds 
of things wouldn't break on the system -- like cron running duplicate 
jobs, etc. OpenLDAP tests would be the least of someone's worries in 
that situation :-)

Given this assumption, then "sleep 10" on a VM should always sleep for 
at *least* 10 seconds as marked by the VM's system clock. It doesn't 
matter how that compares to 10 seconds in the real world, since 
everything running on the VM is calculated relative to the VM clock. In 
particular, both the slapd process and the test shell script are relying 
on the same VM clock. So I don't see how sleeping for "1 second more 
than needed" -- which in this case would be 16 seconds and 31 seconds 
for each section -- could cause anything to break in this particular script.

What am I missing?

Thanks,

     -Kartik