mac80211: fix addba timer

The addba timer function acquires the sta spinlock,
but at the same time we try to del_timer_sync() it
under the spinlock which can produce deadlocks.

To fix this, always del_timer_sync() the timer in
ieee80211_process_addba_resp() and add it again
after checking the conditions, if necessary.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/agg-tx.c

@@ -666,26 +666,25 @@ void ieee80211_process_addba_resp(struct ieee80211_local *local,
 
 	state = &sta->ampdu_mlme.tid_state_tx[tid];
 
+	del_timer_sync(&sta->ampdu_mlme.tid_tx[tid]->addba_resp_timer);
+
 	spin_lock_bh(&sta->lock);
 
-	if (!(*state & HT_ADDBA_REQUESTED_MSK)) {
-		spin_unlock_bh(&sta->lock);
-		return;
-	}
+	if (!(*state & HT_ADDBA_REQUESTED_MSK))
+		goto timer_still_needed;
 
 	if (mgmt->u.action.u.addba_resp.dialog_token !=
 		sta->ampdu_mlme.tid_tx[tid]->dialog_token) {
-		spin_unlock_bh(&sta->lock);
 #ifdef CONFIG_MAC80211_HT_DEBUG
 		printk(KERN_DEBUG "wrong addBA response token, tid %d\n", tid);
 #endif /* CONFIG_MAC80211_HT_DEBUG */
-		return;
+		goto timer_still_needed;
 	}
 
-	del_timer_sync(&sta->ampdu_mlme.tid_tx[tid]->addba_resp_timer);
 #ifdef CONFIG_MAC80211_HT_DEBUG
 	printk(KERN_DEBUG "switched off addBA timer for tid %d \n", tid);
 #endif /* CONFIG_MAC80211_HT_DEBUG */
+
 	if (le16_to_cpu(mgmt->u.action.u.addba_resp.status)
 			== WLAN_STATUS_SUCCESS) {
 		u8 curstate = *state;
@@ -699,5 +698,11 @@ void ieee80211_process_addba_resp(struct ieee80211_local *local,
 	} else {
 		___ieee80211_stop_tx_ba_session(sta, tid, WLAN_BACK_INITIATOR);
 	}
+
+	goto out;
+
+ timer_still_needed:
+	add_timer(&sta->ampdu_mlme.tid_tx[tid]->addba_resp_timer);
+ out:
 	spin_unlock_bh(&sta->lock);
 }