Periodic jobs triggering panics in 10.1 and 10.2

[Jan Bramkamp]

On 09/12/15 01:04, Michael B. Eichorn wrote:
> On Tue, 2015-12-08 at 16:31 -0600, Dustin Wenz wrote:
>> I suspect this is a zfs bug that is triggered by the access patterns
>> in the periodic scripts. There is significant load on the system when
>> the scheduled processes start, because all jails execute the same
>> scripts at the same time.
>>
>> I've been able to alleviate this problem by disabling the security
>> scans within the jails, but leave it enabled on the root host.
>
> To avoid the problem of jails all starting things at the same time, use
> the cron(8) flags -j and -J to set a 'jitter' which will cause cron to
> sleep for a random period of specified duration (60 sec max). Cron
> flags can be set using the rc.conf variable 'cron_flags'.

While jitter would reduce the resource contention a thundering herd of 
cronjobs shouldn't cause the kernel to divide by zero. Spreading the 
load by introducing jitter to cronjobs might hide the problem, but it 
still needs further analysis.

@Dustin Wenz: Can you reproduce the problem and file a PR to track this?