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SubjectRe: [PATCH 09/11] bluetooth: hci_ldisc: fix deadlock condition
On 20/03/14 19:30, Felipe Balbi wrote:
> LDISCs shouldn't call tty->ops->write() from within
> ->write_wakeup().
>
> ->write_wakeup() is called with port lock taken and
> IRQs disabled, tty->ops->write() will try to acquire
> the same port lock and we will deadlock.
>
I think the work queue should be placed into hci_uart_tty_wakeup() and
not hci_uart_tx_wakeup() as added by this patch.

The reason is that the kernel thread hci_uart_send_frame() calls
hci_uart_tx_wakeup() and this patch unnecessarily introduces a work
queue in the program flow of that kernel thread.

In other words, I think this patch has undesirable side-effects such as
adding latency and increased processor loading for hci_uart_send_frame().

Regards,
Dean

> Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
> Reported-by: Huang Shijie <b32955@freescale.com>
> Signed-off-by: Felipe Balbi <balbi@ti.com>
> ---
> drivers/bluetooth/hci_ldisc.c | 24 +++++++++++++++++++-----
> drivers/bluetooth/hci_uart.h | 1 +
> 2 files changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index 6e06f6f..77af52f 100644
> --- a/drivers/bluetooth/hci_ldisc.c
> +++ b/drivers/bluetooth/hci_ldisc.c
> @@ -118,10 +118,6 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)
>
> int hci_uart_tx_wakeup(struct hci_uart *hu)
> {
> - struct tty_struct *tty = hu->tty;
> - struct hci_dev *hdev = hu->hdev;
> - struct sk_buff *skb;
> -
> if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state)) {
> set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
> return 0;
> @@ -129,6 +125,22 @@ int hci_uart_tx_wakeup(struct hci_uart *hu)
>
> BT_DBG("");
>
> + schedule_work(&hu->write_work);
> +
> + return 0;
> +}
> +
> +static void hci_uart_write_work(struct work_struct *work)
> +{
> + struct hci_uart *hu = container_of(work, struct hci_uart, write_work);
> + struct tty_struct *tty = hu->tty;
> + struct hci_dev *hdev = hu->hdev;
> + struct sk_buff *skb;
> +
> + /* REVISIT: should we cope with bad skbs or ->write() returning
> + * and error value ?
> + */
> +
> restart:
> clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
>
> @@ -153,7 +165,6 @@ restart:
> goto restart;
>
> clear_bit(HCI_UART_SENDING, &hu->tx_state);
> - return 0;
> }
>
> static void hci_uart_init_work(struct work_struct *work)
> @@ -281,6 +292,7 @@ static int hci_uart_tty_open(struct tty_struct *tty)
> tty->receive_room = 65536;
>
> INIT_WORK(&hu->init_ready, hci_uart_init_work);
> + INIT_WORK(&hu->write_work, hci_uart_write_work);
>
> spin_lock_init(&hu->rx_lock);
>
> @@ -318,6 +330,8 @@ static void hci_uart_tty_close(struct tty_struct *tty)
> if (hdev)
> hci_uart_close(hdev);
>
> + cancel_work_sync(&hu->write_work);
> +
> if (test_and_clear_bit(HCI_UART_PROTO_SET, &hu->flags)) {
> if (hdev) {
> if (test_bit(HCI_UART_REGISTERED, &hu->flags))
> diff --git a/drivers/bluetooth/hci_uart.h b/drivers/bluetooth/hci_uart.h
> index fffa61f..12df101 100644
> --- a/drivers/bluetooth/hci_uart.h
> +++ b/drivers/bluetooth/hci_uart.h
> @@ -68,6 +68,7 @@ struct hci_uart {
> unsigned long hdev_flags;
>
> struct work_struct init_ready;
> + struct work_struct write_work;
>
> struct hci_uart_proto *proto;
> void *priv;



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