mac80211: clean up sta_info_destroy() users wrt. RCU/locking

Calling sta_info_destroy() doesn't require RCU-synchronisation
before-hand because it does that internally. However, it does
require rtnl-locking so insert that where necessary.

Also clean up the code doing it internally to be a bit clearer and
not synchronize twice if keys are configured.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/cfg.c

@@ -700,11 +700,7 @@ static int ieee80211_del_station(struct wiphy *wiphy, struct net_device *dev,
 			return -ENOENT;
 
 		sta_info_unlink(&sta);
-
-		if (sta) {
-			synchronize_rcu();
-			sta_info_destroy(sta);
-		}
+		sta_info_destroy(sta);
 	} else
 		sta_info_flush(local, sdata);
 

net/mac80211/ieee80211_sta.c

@@ -939,7 +939,6 @@ static void ieee80211_associated(struct net_device *dev,
 	rcu_read_unlock();
 
 	if (disassoc && sta) {
-		synchronize_rcu();
 		rtnl_lock();
 		sta_info_destroy(sta);
 		rtnl_unlock();

net/mac80211/sta_info.c

@@ -180,13 +180,22 @@ void sta_info_destroy(struct sta_info *sta)
 		mesh_plink_deactivate(sta);
 #endif
 
-	/*
-	 * NOTE: This will call synchronize_rcu() internally to
-	 * make sure no key references can be in use. We rely on
-	 * that here for the mesh code!
-	 */
-	ieee80211_key_free(sta->key);
-	WARN_ON(sta->key);
+	if (sta->key) {
+		/*
+		 * NOTE: This will call synchronize_rcu() internally to
+		 * make sure no key references can be in use. We rely on
+		 * that when we take this branch to make sure nobody can
+		 * reference this STA struct any longer!
+		 */
+		ieee80211_key_free(sta->key);
+		WARN_ON(sta->key);
+	} else {
+		/*
+		 * Make sure that nobody can reference this STA struct
+		 * any longer.
+		 */
+		synchronize_rcu();
+	}
 
 #ifdef CONFIG_MAC80211_MESH
 	if (ieee80211_vif_is_mesh(&sta->sdata->vif))
@@ -628,11 +637,9 @@ static void sta_info_debugfs_add_work(struct work_struct *work)
 		rate_control_add_sta_debugfs(sta);
 
 		sta = __sta_info_unpin(sta);
-
-		if (sta) {
-			synchronize_rcu();
-			sta_info_destroy(sta);
-		}
+		rtnl_lock();
+		sta_info_destroy(sta);
+		rtnl_unlock();
 	}
 }
 #endif
@@ -694,8 +701,6 @@ int sta_info_flush(struct ieee80211_local *local,
 	}
 	spin_unlock_irqrestore(&local->sta_lock, flags);
 
-	synchronize_rcu();
-
 	list_for_each_entry_safe(sta, tmp, &tmp_list, list)
 		sta_info_destroy(sta);