mac80211: sync acccess to tx_filtered/ps_tx_buf queues

These are accessed without a lock when ending STA PSM. If the
sta_cleanup timer accesses these lists at the same time, we might crash.

This may fix some mysterious crashes we had during
ieee80211_sta_ps_deliver_wakeup.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Ido Yariv <ido@wizery.com>

net/mac80211/sta_info.c

@@ -961,6 +961,7 @@ void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
 	struct ieee80211_local *local = sdata->local;
 	struct sk_buff_head pending;
 	int filtered = 0, buffered = 0, ac;
+	unsigned long flags;
 
 	clear_sta_flag(sta, WLAN_STA_SP);
 
@@ -976,12 +977,16 @@ void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
 	for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
 		int count = skb_queue_len(&pending), tmp;
 
+		spin_lock_irqsave(&sta->tx_filtered[ac].lock, flags);
 		skb_queue_splice_tail_init(&sta->tx_filtered[ac], &pending);
+		spin_unlock_irqrestore(&sta->tx_filtered[ac].lock, flags);
 		tmp = skb_queue_len(&pending);
 		filtered += tmp - count;
 		count = tmp;
 
+		spin_lock_irqsave(&sta->ps_tx_buf[ac].lock, flags);
 		skb_queue_splice_tail_init(&sta->ps_tx_buf[ac], &pending);
+		spin_unlock_irqrestore(&sta->ps_tx_buf[ac].lock, flags);
 		tmp = skb_queue_len(&pending);
 		buffered += tmp - count;
 	}