Re: [PATCH 2/5] net: Make rtnetlink infrastructure network namespace aware

Eric W. Biederman wrote:

 void rtnl_unlock(void)
 {
-	mutex_unlock(&rtnl_mutex);
-	if (rtnl && rtnl->sk_receive_queue.qlen)
+	struct net *net;
+
+	/*
+	 * Loop through all of the rtnl sockets until none of them (in
+	 * a live network namespace) have queue packets.
+	 *
+	 * We have to be careful with the locking here as
+	 * sk_data_ready aka rtnetlink_rcv takes the rtnl_mutex.
+	 *
+	 * To ensure the network namespace does not exit while
+	 * we are processing packets on it's rtnl socket we
+	 * grab a reference to the network namespace, ignoring
+	 * it if the network namespace has already exited.
+	 */
+retry:
+	for_each_net(net) {
+		struct sock *rtnl = net->rtnl;
+
+		if (!rtnl || !rtnl->sk_receive_queue.qlen)
+			continue;
+
+		if (!maybe_get_net(net))
+			continue;
+
+		mutex_unlock(&rtnl_mutex);
 		rtnl->sk_data_ready(rtnl, 0);
+		mutex_lock(&rtnl_mutex);
+		put_net(net);
+		goto retry;
+	}
+	mutex_unlock(&rtnl_mutex);
+
 	netdev_run_todo();
 }

I'm wondering why this receive queue processing on unlock is still
necessary today, we don't do trylock in rtnetlink_rcv anymore, so
all senders will simply wait until the lock is released and then
process the queue.