virtio: console: add locking in port unplug path

Port unplug can race with close() in port_fops_release().
port_fops_release() already takes the necessary locks, ensure
unplug_port() does that too.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

drivers/char/virtio_console.c

@@ -1542,6 +1542,7 @@ static void unplug_port(struct port *port)
 	list_del(&port->list);
 	spin_unlock_irq(&port->portdev->ports_lock);
 
+	spin_lock_irq(&port->inbuf_lock);
 	if (port->guest_connected) {
 		port->guest_connected = false;
 		port->host_connected = false;
@@ -1550,6 +1551,7 @@ static void unplug_port(struct port *port)
 		/* Let the app know the port is going down. */
 		send_sigio_to_port(port);
 	}
+	spin_unlock_irq(&port->inbuf_lock);
 
 	if (is_console_port(port)) {
 		spin_lock_irq(&pdrvdata_lock);