Bug 188576

Description Adrian Chadd 2014-04-14 00:30:00 UTC

Whenever an ath(4) 11n station reassociates or downgrades from aggregation to no aggregation, there's a chance that it'll hang and refuse to queue more frames.

The session needs to be fully torn down (eg ifconfig wlanX down) for things to go back to normal.

Fix: 

I actually have debugged this a little already.

So the problem seems to be that there's more than one entry point into ath_tx_tid_cleanup(). It's likely a couple of calls into the reassociation path or one into reassociate and one into aggregation teardown. I'll go figure that bit out soon.

But what it leads to is thus:

* the caller causes ath_tx_tid_pause();
* ath_tx_tid_cleanup() is called;
* the first time this happens it sees there's 1 or more frames to cleanup, so it sets tid->cleanup_inprogress;
* the caller then checks if that's set to 1 - if so, it assumes that it should wait until the cleanup is finished;
* otherwise it calls ath_tx_tid_resume().

If tid->cleanup_inprogress is set to 1 then the normal TX completion path will eventually call ath_tx_comp_cleanup_unaggr() or ath_tx_comp_cleanup_aggr() which will clear the flag and resume the TID.

If a second path through ath_tx_tid_cleanup() occurs, then:

* the caller pauses;
* ath_tx_tid_cleanup() is called;
* tid->cleanup_inprogress is set to 1, but there's no code to check whether this call actually set it or not - so it doesn't call ath_tx_tid_resume().

So once the frames complete and ath_tx_tid_resume() is called, there's still a pending paused reference and thus traffic never continues flowing.