mac80211: Speedup ieee80211_remove_interfaces()

Speedup ieee80211_remove_interfaces() by factorizing synchronize_rcu() calls
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Reviewed-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/mac80211/iface.c

@@ -860,22 +860,18 @@ void ieee80211_if_remove(struct ieee80211_sub_if_data *sdata)
 void ieee80211_remove_interfaces(struct ieee80211_local *local)
 {
 	struct ieee80211_sub_if_data *sdata, *tmp;
+	LIST_HEAD(unreg_list);
 
 	ASSERT_RTNL();
 
+	mutex_lock(&local->iflist_mtx);
 	list_for_each_entry_safe(sdata, tmp, &local->interfaces, list) {
-		/*
-		 * we cannot hold the iflist_mtx across unregister_netdevice,
-		 * but we only need to hold it for list modifications to lock
-		 * out readers since we're under the RTNL here as all other
-		 * writers.
-		 */
-		mutex_lock(&local->iflist_mtx);
 		list_del(&sdata->list);
-		mutex_unlock(&local->iflist_mtx);
 
-		unregister_netdevice(sdata->dev);
+		unregister_netdevice_queue(sdata->dev, &unreg_list);
 	}
+	mutex_unlock(&local->iflist_mtx);
+	unregister_netdevice_many(&unreg_list);
 }
 
 static u32 ieee80211_idle_off(struct ieee80211_local *local,