bluetooth: hci_ldisc: fix deadlock condition

commit da64c27d upstream.

LDISCs shouldn't call tty->ops->write() from within
->write_wakeup().

->write_wakeup() is called with port lock taken and
IRQs disabled, tty->ops->write() will try to acquire
the same port lock and we will deadlock.
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Reported-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Tested-by: Andreas Bießmann <andreas@biessmann.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/bluetooth/hci_ldisc.c

@@ -120,10 +120,6 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)
 
 int hci_uart_tx_wakeup(struct hci_uart *hu)
 {
-	struct tty_struct *tty = hu->tty;
-	struct hci_dev *hdev = hu->hdev;
-	struct sk_buff *skb;
-
 	if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state)) {
 		set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
 		return 0;
@@ -131,6 +127,22 @@ int hci_uart_tx_wakeup(struct hci_uart *hu)
 
 	BT_DBG("");
 
+	schedule_work(&hu->write_work);
+
+	return 0;
+}
+
+static void hci_uart_write_work(struct work_struct *work)
+{
+	struct hci_uart *hu = container_of(work, struct hci_uart, write_work);
+	struct tty_struct *tty = hu->tty;
+	struct hci_dev *hdev = hu->hdev;
+	struct sk_buff *skb;
+
+	/* REVISIT: should we cope with bad skbs or ->write() returning
+	 * and error value ?
+	 */
+
 restart:
 	clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
 
@@ -155,7 +167,6 @@ int hci_uart_tx_wakeup(struct hci_uart *hu)
 		goto restart;
 
 	clear_bit(HCI_UART_SENDING, &hu->tx_state);
-	return 0;
 }
 
 /* ------- Interface to HCI layer ------ */
@@ -274,6 +285,8 @@ static int hci_uart_tty_open(struct tty_struct *tty)
 	hu->tty = tty;
 	tty->receive_room = 65536;
 
+	INIT_WORK(&hu->write_work, hci_uart_write_work);
+
 	spin_lock_init(&hu->rx_lock);
 
 	/* Flush any pending characters in the driver and line discipline. */
@@ -308,6 +321,8 @@ static void hci_uart_tty_close(struct tty_struct *tty)
 		if (hdev)
 			hci_uart_close(hdev);
 
+		cancel_work_sync(&hu->write_work);
+
 		if (test_and_clear_bit(HCI_UART_PROTO_SET, &hu->flags)) {
 			if (hdev) {
 				hci_unregister_dev(hdev);

drivers/bluetooth/hci_uart.h

@@ -64,6 +64,8 @@ struct hci_uart {
 	unsigned long		flags;
 	unsigned long		hdev_flags;
 
+	struct work_struct	write_work;
+
 	struct hci_uart_proto	*proto;
 	void			*priv;