--- x/drivers/bluetooth/hci_uart.h
+++ y/drivers/bluetooth/hci_uart.h
@@ -69,6 +69,7 @@ struct hci_uart {
 	unsigned long		hdev_flags;
 
 	struct work_struct	init_ready;
+	struct mutex 		write_mutex;
 	struct work_struct	write_work;
 
 	const struct hci_uart_proto *proto;
--- x/drivers/bluetooth/hci_ldisc.c
+++ y/drivers/bluetooth/hci_ldisc.c
@@ -154,6 +154,7 @@ static void hci_uart_write_work(struct w
 	/* REVISIT: should we cope with bad skbs or ->write() returning
 	 * and error value ?
 	 */
+	mutex_lock(&hu->write_mutex);
 
 restart:
 	clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
@@ -180,6 +181,7 @@ restart:
 		goto restart;
 
 	wake_up_bit(&hu->tx_state, HCI_UART_SENDING);
+	mutex_unlock(&hu->write_mutex);
 }
 
 void hci_uart_init_work(struct work_struct *work)
@@ -515,6 +517,7 @@ static int hci_uart_tty_open(struct tty_
 
 	INIT_WORK(&hu->init_ready, hci_uart_init_work);
 	INIT_WORK(&hu->write_work, hci_uart_write_work);
+	mutex_init(&hu->write_mutex);
 
 	/* Flush any pending characters in the driver */
 	tty_driver_flush_buffer(tty);