somewhat reproducable vimage panic

[Hans Petter Selasky]

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