Re: [PATCH] ath9k : Fix ieee80211 work while going to suspend

On Thu, Mar 21, 2013 at 12:33:31PM -0700, Luis R. Rodriguez wrote:

So when does this work get called?

Given the trace this is hit when the timer rx_poll_timer runs,
which in turn calls ath_rx_poll() to schedule hw_check_work work.
The rx_poll_timer however was originally only set at the end of
the routine that hw_check_work sets off but also at other entry
points (ath_start_rx_poll() callers). Once ath_start_rx_poll()
gets called though we can go on looping as follows:

work			timer			work
hw_check_work	-->	rx_poll_timer	-->	hw_check_work

At suspend time we do this though:

ath_cancel_work(sc);                                                    
del_timer_sync(&sc->rx_poll_timer);  
 
+	del_timer_sync(&sc->rx_poll_timer);
 	ath_cancel_work(sc);
 	ath_stop_ani(sc);
-	del_timer_sync(&sc->rx_poll_timer);

[snip]

But then we have the chicken and the egg problem, as the work item
could fire off the timer so it would seem to be good to prevent
adding new work when suspending.

Yup, this is egg and chicken problem, I think it can not be fixed by
changing ordering of del_timer and cancel_work, it would be like:

del_timer_sync(&sc->rx_poll_timer);
/* but timer could schedule work */
ath_cancel_work(sc);
/* but work could schedule timer */ 
del_timer_sync(&sc->rx_poll_timer);
/* but timer could schedule work */
ath_cancel_work(sc);
/* And so on ... */

Check is needed in work or timer callback, depending what is canceled
last, to fix the problem ...

quoted

In mac80211 we use local->suspended and local->quiesce booleans to
prevent reschedule of timers when going to suspend for example.
Works use ifmgd->associted to prevent reschedule when we are
disassociating.

I think on ath9k also some boolean variable should be used, not only
for rx_poll_timer but also for other works i.e. tx_complete_work.
Is possible to use SC_OP_INVALID flags, since mac80211 call ath9k_stop
on suspend and ath9k_start on resume.

Indeed however ieee80211_queue_work() already does a suspend check for
us, it just complains as many drivers including mac80211 were setting
up work incorrectly. The warning was put in place to help us find the
issues. Using SC_OP_INVALID seems fair but we could also add a routine
ieee80211_queue_work_safe() that silently fails if we are quiescing or
suspended and not resuming but I can see that creating very sloppy
driver writing and everyone abusing it.

We also have to reliable cancel works on ath9k_stop() if device goes
down for other reason than suspend, new mac80211 ieee80211_queue_work_safe()
routine will not help with that.

That looks ok for me as -stable fix

Reviewed-by: Stanislaw Gruszka <redacted>

Stanislaw 
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