somewhat reproducable vimage panic

[Kristof Provost]

On 23 Jul 2020, at 11:00, Bjoern A. Zeeb wrote:
> On 23 Jul 2020, at 8:09, Kristof Provost wrote:
>
>> On 23 Jul 2020, at 9:19, Kristof Provost wrote:
>>> On 23 Jul 2020, at 0:15, John-Mark Gurney wrote:
>>>> So, it's pretty easy to trigger, just attach a couple USB ethernet
>>>> adapters, in my case, they were ure, but likely any two spare 
>>>> ethernet
>>>> interfaces will work, and wire them back to back..
>>>>
>>> I’ve been able to trigger it using epair as well:
>>>
>>> `sudo sh testinterfaces.txt epair0a epair0b`
>>>
>>> I did have to comment out the waitcarrier() check.
>>>
>> I’ve done a little bit of digging, and I think I’m starting to 
>> see how this breaks.
>>
>> This always affects the jailed vlan interfaces. They’re getting 
>> deleted, but the ifp doesn’t go away just yet because it’s still 
>> in use by the multicast code.
>> The multicast code does its cleanup in task queues,
>
> Wow, did I miss that back then? Did I review a change and not notice? 
> Sorry if that was the case.
>
> Vnet teardown is blocking and forceful.
> Doing deferred cleanup work isn’t a good idea at all.
> I think that is the real problem here.
>
> I’d rather have us fix this than putting more bandaids into the 
> code.
>
Yeah, agreed. I think hselasky has a better fix: 
https://reviews.freebsd.org/D24914

I just saw his e-mail in a different thread.

Best regards,
Kristof