Periodic jobs triggering panics in 10.1 and 10.2

[Dustin Wenz]

PF filed:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=205163

Please let me know if there is any more useful information I can include.

	- .Dustin Wenz


> On Dec 9, 2015, at 4:24 AM, Jan Bramkamp <crest at rlwinm.de> wrote:
> 
> 
> 
> 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?
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