Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup()
authorDean Jenkins <Dean_Jenkins@mentor.com>
Fri, 28 Apr 2017 12:57:26 +0000 (13:57 +0100)
committerMarcel Holtmann <marcel@holtmann.org>
Sun, 30 Apr 2017 10:22:14 +0000 (12:22 +0200)
commit2d6f1da168e1d62c47f7d50135ac4cbd8411dcb1
tree5c30f562bc90fd01a73e840e2b68697af92ca6e7
parent048e1bd3a27fbeb84ccdff52e165370c1339a193
Bluetooth: hci_ldisc: Add protocol check to hci_uart_tx_wakeup()

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>
drivers/bluetooth/hci_ldisc.c