Re: Any /n NICs that support APs and multiple STAs other than ath9k?

[Ben Greear <greearb@candelatech.com>]

On 10/06/2010 11:58 AM, Luis R. Rodriguez wrote:
> On Wed, Oct 6, 2010 at 11:49 AM, Ben Greear<greearb@candelatech.com>  wrote:
>> On 10/06/2010 11:45 AM, Luis R. Rodriguez wrote:
>>>
>>> On Wed, Oct 6, 2010 at 9:29 AM, Ben Greear<greearb@candelatech.com>
>>>   wrote:
>>>>
>>>> I would like to have a different hardware/driver combination to try
>>>> to tie-break whether bugs are in mac80211 or in the ath9k
>>>> driver/hardware.
>>>>
>>>> I don't mind doing a bit of driver hacking so long as the basic support
>>>> is there (I think it's mostly the ability to set a BSSID mask and
>>>> rxfilter
>>>> accordingly).
>>>
>>> Your best bet is to test against mac80211_hwsim, that would rule out
>>> any hardware. I think Jouni and Johannes have also a way to get the
>>> devices to talk to each other. Perhaps some documentation of that on
>>> the kernel Documentation/networking/mac80211_hwsim/
>>
>> Ok.  I'm trying to hack slub to give me a better stack trace of where
>> the skb was deleted.  If that doesn't turn up anything obvious, then
>> I'll go read up on hwsim.
>>
>> Are you aware of any DMA issues that might cause ath9k to write into
>> places it should not?  Previously, I've seen a lot of errors in
>> the logs about ath9k not being able to stop DMA in time, but I haven't
>> seen those while reproducing the memory corruption.
>
> Yeah, well there have been a few bug reports but when we asked for
> instructions how to reproduce we get nowhere. You are the first to
> actually find some reproducible instructions. Forgive me but I haven't
> had time yet to work on this though. Seems you have a good grasp of
> things though and can easily reproduce so you likely are in a better
> position right now to debug at the moment.

My understanding is that the bad DMA access could
corrupt things right out from under slub, and with no way for me
to possibly add any debugging to catch it in action.

I'm quite ignorant of hardware, DMA issues, etc, so if you have any
ideas on how to go about verifying bad DMA writes or not, I'm
interested.

Otherwise, I'll basically have to check and double check to make sure
we don't have a normal use-after-free with the skb, and if I can't find
anything, just assert that it's DMA issues and pretty much give up until
someone that understands that stuff has an idea to try.

Thanks,
Ben

>
>    Luis


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com