Bluetooth: Remove useless rx_lock spinlock

rx_lock spinlock is only used in hci_uart_tty_receive() which is the
receive_buf ldisc callback.

hci_uart_tty_receive() is protected from re-entrance by its only
caller (flush_to_ldisc() in drivers/tty/tty_buffer.c) which held a
mutex (buf->lock) for this section.
This lock allows "safe use of the line discipline's receive_buf()
method by excluding the buffer work and any pending flush from using
the flip buffer." (comments from tty_buffer_lock_exclusive() in
drivers/tty/tty_buffer.c)

So, no need to double protect this resource with rx_lock.

Signed-off-by: Frederic Danis <frederic.danis@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/hci_ldisc.c

@@ -470,8 +470,6 @@ static int hci_uart_tty_open(struct tty_struct *tty)
 	INIT_WORK(&hu->init_ready, hci_uart_init_work);
 	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. */
 
 	/* FIXME: why is this needed. Note don't use ldisc_ref here as the
@@ -569,14 +567,14 @@ static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data,
 	if (!test_bit(HCI_UART_PROTO_SET, &hu->flags))
 		return;
 
-	spin_lock(&hu->rx_lock);
+	/* It does not need a lock here as it is already protected by a mutex in
+	 * tty caller
+	 */
 	hu->proto->recv(hu, data, count);
 
 	if (hu->hdev)
 		hu->hdev->stat.byte_rx += count;
 
-	spin_unlock(&hu->rx_lock);
-
 	tty_unthrottle(tty);
 }
 

drivers/bluetooth/hci_uart.h

@@ -85,7 +85,6 @@ struct hci_uart {
 
 	struct sk_buff		*tx_skb;
 	unsigned long		tx_state;
-	spinlock_t		rx_lock;
 
 	unsigned int init_speed;
 	unsigned int oper_speed;