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Date:      Thu, 23 Jul 2020 19:26:38 +0000
From:      "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net>
To:        "Kristof Provost" <kp@FreeBSD.org>, "Hans Petter Selasky" <hselasky@FreeBSD.org>
Cc:        "John-Mark Gurney" <jmg@funkthat.com>, freebsd-net@freebsd.org, freebsd-current@freebsd.org
Subject:   Re: somewhat reproducable vimage panic
Message-ID:  <B881F5AC-90A0-4B50-9645-20D6291A5CED@lists.zabbadoz.net>
In-Reply-To: <F1A36FB1-D958-42A8-9F32-838F2D8D805D@FreeBSD.org>
References:  <20200721091654.GC4213@funkthat.com> <20200721113153.42d83119@x23> <20200721202323.GE4213@funkthat.com> <38F5A3A6-B578-4BA4-8F69-C248163CB6E0@libassi.se> <20200722060514.GF4213@funkthat.com> <20200722193443.GG4213@funkthat.com> <6C149617-55BB-4A87-B993-195E5E133790@lists.zabbadoz.net> <20200722221509.GI4213@funkthat.com> <2FFC49F9-83DE-4FA1-A47F-1D8A7AF4B241@FreeBSD.org> <6847FB6B-0B1A-43C7-B567-15BF21AB5D56@FreeBSD.org> <8B72C0B9-9CF0-4557-81D7-77190775805C@lists.zabbadoz.net> <F1A36FB1-D958-42A8-9F32-838F2D8D805D@FreeBSD.org>

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On 23 Jul 2020, at 9:02, Kristof Provost wrote:

> 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.

That’ll probably work;  still, the deferred teardown work seems wrong 
to me;  I haven’t investigated;  the patch kind-of says exactly that 
as well: if “wait until deferred stuff is done” is all we are doing, 
why can we not do it on the spot then?

/bz




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