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    Subject[PATCH AUTOSEL for 4.9 124/190] Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup()
    Date
    From: Dean Jenkins <Dean_Jenkins@mentor.com>

    [ 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.

    Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com>
    Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    drivers/bluetooth/hci_ldisc.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
    index 7ec73945351c..2230f9368c21 100644
    --- a/drivers/bluetooth/hci_ldisc.c
    +++ b/drivers/bluetooth/hci_ldisc.c
    @@ -125,6 +125,9 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)

    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;
    --
    2.14.1
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