Patch "Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
bluetooth-hci_ldisc-add-protocol-check-to-hci_uart_tx_wakeup.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dean Jenkins <[email protected]>
Date: Fri, 28 Apr 2017 13:57:26 +0100
Subject: Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup()

From: Dean Jenkins <[email protected]>

[ Upstream commit 2d6f1da168e1d62c47f7d50135ac4cbd8411dcb1 ]

Before attempting to schedule a work-item onto hu->write_work in hci_uart_tx_wakeup(), check that the Data Link protocol layer is still bound to the HCI UART driver.

Failure to perform this protocol check causes a race condition between the work queue hu->write_work running hci_uart_write_work() and the Data Link protocol layer being unbound (closed) in hci_uart_tty_close().

Note hci_uart_tty_close() does have a "cancel_work_sync(&hu->write_work)" but it is ineffective because it cannot prevent work-items being added to hu->write_work after cancel_work_sync() has run.

Therefore, add a check for HCI_UART_PROTO_READY into hci_uart_tx_wakeup() which prevents scheduling of the work queue when HCI_UART_PROTO_READY is in the clear state. However, note a small race condition remains because the hci_uart_tx_wakeup() thread can run in parallel with the hci_uart_tty_close() thread so it is possible that a schedule of hu->write_work can occur when HCI_UART_PROTO_READY is cleared. A complete solution needs locking of the threads which is implemented in a future commit.

---
 drivers/bluetooth/hci_ldisc.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -125,6 +125,9 @@ static inline struct sk_buff *hci_uart_d
 
 int hci_uart_tx_wakeup(struct hci_uart *hu)
 {
+	if (!test_bit(HCI_UART_PROTO_READY, &hu->flags))
+		return 0;
+
 	if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state)) {
 		set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
 		return 0;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/bluetooth-hci_ldisc-add-protocol-check-to-hci_uart_dequeue.patch queue-4.9/bluetooth-hci_ldisc-add-protocol-check-to-hci_uart_tx_wakeup.patch