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Date: Tue, 17 Mar 2009 12:02:42 -0700
From: Sam Leffler <sam@freebsd.org>
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To: Bruce Simpson <bms@incunabulum.net>
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Cc: current@freebsd.org, Coleman Kane <cokane@freebsd.org>,
	freebsd-net <net@freebsd.org>
Subject: Re: IGMP+WiFi panic on recent kernel - in igmp_fasttimo()
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Bruce Simpson wrote:
> Coleman Kane wrote:
>> If you are looking for a reliable test case, this might be it for you,
>> but I think you need a wlan interface to test it with:
>>   * Install net/avahi from ports
>>   * Set avahi_daemon_enable="YES" in rc.conf
>>   * Configure VAP params for wlan0 card in rc.conf
>>   * Log in and run "dhclient wlan0" to trigger the panic
>>
>>   
>
> Actually I was able to panic the kernel right away with the 802.11 
> code, just
> by joining a multicast group with mtest(8) on the wlan interface.
>
> i.e.
>
> # mtest
> j 224.0.0.2 192.168.x.x
> -> boom
>
> I believe I've found the symptom, but the root cause I don't fully 
> understand.
> Sam indicated that the VAP code is using ifma's in some nested way 
> between
> the ifnets which comprise the VAP's member interfaces.
>
> A workaround is pending....
>

net80211 uses the public api's to push mcast addresses from the vap's to 
the parent ifnet.  It does not directly frob any internal data 
structures except to workaround the ioctl-based callback out of the 
mcast code when adding an address.  Look at ieee80211_ioctl_updatemulti 
for details.

    Sam