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Date:	Thu, 20 Mar 2014 14:21:17 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	balbi@...com
CC:	Marcel Holtmann <marcel@...tmann.org>,
	Alan Cox <alan@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Muralidharan Karicheri <m-karicheri2@...com>,
	linux-bluetooth@...r.kernel.org, linux-serial@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Huang Shijie <b32955@...escale.com>
Subject: Re: hci_ldsic nested locking problem

On 03/20/2014 02:11 PM, Felipe Balbi wrote:
> On Thu, Mar 20, 2014 at 01:31:40PM -0400, Peter Hurley wrote:
>> [ +cc Huang Shijie ]
>>
>> On 03/20/2014 01:16 PM, Felipe Balbi wrote:
>>> On Thu, Mar 20, 2014 at 04:42:16PM +0000, Alan Cox wrote:
>>>> On Thu, 2014-03-20 at 11:34 -0500, Felipe Balbi wrote:
>>>>> Hi,
>>>>>
>>>>> when 8250 driver calls uart_write_wakeup(), the tty port lock is already
>>>>> taken. hci_ldisc.c's implementation of ->write_wakeup() calls
>>>>> tty->ops->write() to actually send the characters, but that call will
>>>>> try to acquire the same port lock again.
>>>>>
>>>>> Looking at other line disciplines that looks like a bug in hci_ldisc.c.
>>>>> Am I correct to assume that ->write_wakeup() is supposed to *just*
>>>>> wakeup the bottom half so we handle ->write() in another context ?
>>>>>
>>>>> Is it legal to call tty->ops->write() from within ->write_wakeup() ?
>>>>
>>>> It isn't because you might send all the bytes and go
>>>>
>>>> 	write
>>>> 		write_wakeup
>>>> 			write
>>>> 				write wakeup
>>>> 					...
>>>>
>>>> and recurse
>>>
>>> cool, so there really is a bug in hci_ldisc. Marcel, any tips on how do
>>> you want this to be sorted out ?
>>
>> hci_uart_tx_wakeup() should perform the I/O as work.
>> FWIW, this was reported by Huang Shijie back on Dec 6.
>>
>> I'd fix it but I have no way to test it.
>
> here's a build-tested only patch which is waiting for testing from other
> colleagues who've got a platform to reproduce the problem:

Where's the cancel_work_sync() on teardown?

Regards,
Peter Hurley

> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index bc68a44..789000d 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 +125,18 @@ 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, init_ready);
> +	struct tty_struct *tty = hu->tty;
> +	struct hci_dev *hdev = hu->hdev;
> +	struct sk_buff *skb;
> +
>   restart:
>   	clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state);
>
> @@ -153,7 +161,6 @@ restart:
>   		goto restart;
>
>   	clear_bit(HCI_UART_SENDING, &hu->tx_state);
> -	return 0;
>   }
>
>   static void hci_uart_init_work(struct work_struct *work)
> @@ -289,6 +296,7 @@ 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);
>
> 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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