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Date:      Mon, 10 Aug 2020 11:46:53 +0200
From:      Hans Petter Selasky <hps@selasky.org>
To:        "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net>, Kristof Provost <kp@FreeBSD.org>
Cc:        John-Mark Gurney <jmg@funkthat.com>, freebsd-net@freebsd.org, freebsd-current@freebsd.org, Stephen Hurd <shurd@FreeBSD.org>
Subject:   Re: somewhat reproducable vimage panic
Message-ID:  <826eb82b-c6f9-9ef0-8dda-14ad00ce183e@selasky.org>
In-Reply-To: <B881F5AC-90A0-4B50-9645-20D6291A5CED@lists.zabbadoz.net>
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> <B881F5AC-90A0-4B50-9645-20D6291A5CED@lists.zabbadoz.net>

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On 2020-07-23 21:26, Bjoern A. Zeeb wrote:
> 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?

Hi Bjoern,

Trying to move the discussion over to Phabricator at:
https://reviews.freebsd.org/D24914

The answer to your question I believe is this commit:

https://svnweb.freebsd.org/base/head/sys/netinet/in_mcast.c?revision=333175&view=markup

It affects both IPv4 and IPv6.

I know that sometimes multicast entries can be freed from timer 
callbacks. I think having a task, probably one is enough, for network 
related configuration is acceptable. With D24914 there will be two 
threads to teardown which is probably overkill, but anyway makes a solid 
solution for now.

I don't know why Stephen didn't think about draining those tasks. I know 
some people are not actively using VIMAGE and that might be the reason.

--HPS



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