mac80211: catch queue stop underflow

If some code stops the queues more times than having started
(for when refcounting is used), warn on and reset the counter
to 0 to avoid blocking forever.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/util.c

@@ -288,10 +288,13 @@ static void __ieee80211_wake_queue(struct ieee80211_hw *hw, int queue,
 	if (!test_bit(reason, &local->queue_stop_reasons[queue]))
 		return;
 
-	if (!refcounted)
+	if (!refcounted) {
 		local->q_stop_reasons[queue][reason] = 0;
-	else
+	} else {
 		local->q_stop_reasons[queue][reason]--;
+		if (WARN_ON(local->q_stop_reasons[queue][reason] < 0))
+			local->q_stop_reasons[queue][reason] = 0;
+	}
 
 	if (local->q_stop_reasons[queue][reason] == 0)
 		__clear_bit(reason, &local->queue_stop_reasons[queue]);