IGMP+WiFi panic on recent kernel - in igmp_fasttimo()

[Bruce Simpson]

Sam Leffler wrote:
> It is the same issue but the root cause is unclear.  There is much 
> code that does assumes ifma_protospec might be NULL and checks for 
> it.  In my case (creating a wlan ifnet and then destroying it on 
> eject) the patch below is sufficient.  I don't care to dig right now 
> to understand how this stuff is supposed to work; it should be clear 
> from comments etc but the code is lacking.
>

    This is just to say I've tried to reproduce the 802.11 related 
panics,  however have hit a brick wall because the PCI-CardBus bridge 
does not seem to detect anything in its slot. (1U Itox Expanding Dragon 
industrial PC w/a SiteCom branded Ricoh RL475 cardbus card). I tried 
unloading if_fxp with IGMPv3 active on the ifnet, and didn't see any 
panic, I'm assuming this is OK for the time being.

    Qing Li volunteered to test IGMPv3 out for any VLAN related issues 
-- I understand it stacks ifnets in a similar way to that of 802.11 -- 
however I have had no feedback from him since last week.
    So I'm waiting for a HEAD build to a USB2 stick to finish, so I can 
try testing nondestructively on my laptop, where I know for sure that 
the PCI-CardBus bridge slot works, and I can detach an 802.11 card on 
the fly.

    Re ifma_protospec: Yes, there are tricks in the ifnet/in layer which 
set it to NULL and look for it to be NULL. I ended up doing it this way 
mainly because adding reference counting to ifnet would have simply been 
too much work, and it's really a ball that needs to be kicked around at 
a dev summit. However time presses on and it's better to get SOMETHING 
out there.
    Most likely the IGMPv3 changes are hitting this in the 802.11 case 
somehow, I don't have a complete picture of how/why/what's going on, and 
have been relying on feedback from others so far.

cheers
BMS