[ath9k-devel] [PATCH] mac80211: debugfs var for the default aggregation timeout.

On Wed, Apr 6, 2016 at 3:40 AM, Johannes Berg <[email protected]> wrote:
> On Tue, 2016-04-05 at 19:46 -0400, Avery Pennarun wrote:
>
>> This test was with backports-20150525 on ath9k.  (We have newer
>> versions in the queue, but they haven't rolled out to our customers
>> yet.  Anyway, earlier in this thread, I was able to trigger the race
>> condition on much newer backports.  Unfortunately the current fix
>> makes my reproducible test case go away, but I don't know any reason
>> to assume the race condition is fixed.)
>
> Well, we know that the timeout is likely unrelated to the issue (other
> than not triggering the broken code path that frequently), so you can
> revert the timeout change for the test case.

Yes.  And I can make it happen more often by making it timeout the
aggregation agreement much more frequently than usual.

>> While we're here, unfortunately it turns out that just observing the
>> agg_status file can cause crashes (though not very often... except
>> for a few unlucky customers), probably due to a different race
>> condition.
>> Any suggestions about this one?  Stack trace attached below.  (I
>> think the stack trace suggests a mac80211 problem?)
>
> That has to be a mac80211 problem, yeah.
> (Side note: I'm a bit surprised this is a 32-bit system?)

We're going for all of good, fast, and cheap here.  That should end well :)

> Looks like we use RCU protection to get the data. Can I get the
> mac80211.ko binary (with debug data) corresponding to the crash below?

Yes.  Here it is:
http://apenwarr.ca/tmp/mac80211-agg-status-crash.ko

Thanks for your help!