Bluetooth: Purge the dlc->tx_queue to avoid circular dependency

In rfcomm_tty_cleanup we purge the dlc->tx_queue which may contain
socket buffers referencing the tty_port and thus preventing the tty_port
destruction.
Signed-off-by: Gianluca Anzolin <gianluca@sottospazio.it>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

net/bluetooth/rfcomm/tty.c

@@ -668,6 +668,12 @@ static void rfcomm_tty_cleanup(struct tty_struct *tty)
 	tty->driver_data = NULL;
 	rfcomm_dlc_unlock(dev->dlc);
 
+	/*
+	 * purge the dlc->tx_queue to avoid circular dependencies
+	 * between dev and dlc
+	 */
+	skb_queue_purge(&dev->dlc->tx_queue);
+
 	tty_port_put(&dev->port);
 }