Hi Dean,
> 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@xxxxxxxxxx>
> ---
> drivers/bluetooth/hci_ldisc.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index c4b801b..a1bb4d64b9 100644
> --- a/drivers/bluetooth/hci_ldisc.c
> +++ b/drivers/bluetooth/hci_ldisc.c
> @@ -125,15 +125,19 @@ 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))
> + goto no_schedule;
> +
> if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state)) {
> set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
> - return 0;
> + goto no_schedule;
> }
>
> BT_DBG("");
>
> schedule_work(&hu->write_work);
>
> +no_schedule:
> return 0;
> }
so instead of calling no_schedule label, just keep calling return 0 directly.
Regards
Marcel
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