[PATCH RFC] tty_ldisc: add more limits to the @write_wakeup

[PATCH RFC] tty_ldisc: add more limits to the @write_wakeup

[Huang Shijie]

In the uart_handle_cts_change(), uart_write_wakeup() is called after
we call @uart_port->ops->start_tx().

The Documentation/serial/driver tells us:
-----------------------------------------------
  start_tx(port)
	Start transmitting characters.

	Locking: port->lock taken.
	Interrupts: locally disabled.
-----------------------------------------------

So when the uart_write_wakeup() is called, the port->lock is taken by
the upper. See the following callstack:

	|_ uart_write_wakeup
	   |_ tty_wakeup
	      |_ ld->ops->write_wakeup

With the port->lock held, we call the @write_wakeup. Some implemetation of
the @write_wakeup does not notice that the port->lock is held, and it still
tries to send data with uart_write() which will try to grab the prot->lock.
A dead lock occurs, see the following log caught in the Bluetooth by uart:

--------------------------------------------------------------------
BUG: spinlock lockup suspected on CPU#0, swapper/0/0
 lock: 0xdc3f4410, .magic: dead4ead, .owner: swapper/0/0, .owner_cpu: 0
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W    3.10.17-16839-ge4a1bef #1320
[<80014cbc>] (unwind_backtrace+0x0/0x138) from [<8001251c>] (show_stack+0x10/0x14)
[<8001251c>] (show_stack+0x10/0x14) from [<802816ac>] (do_raw_spin_lock+0x108/0x184)
[<802816ac>] (do_raw_spin_lock+0x108/0x184) from [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60)
[<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) from [<802f5754>] (uart_write+0x38/0xe0)
[<802f5754>] (uart_write+0x38/0xe0) from [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168)
[<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) from [<802dab18>] (tty_wakeup+0x50/0x5c)
[<802dab18>] (tty_wakeup+0x50/0x5c) from [<802f81a4>] (imx_rtsint+0x50/0x80)
[<802f81a4>] (imx_rtsint+0x50/0x80) from [<802f88f4>] (imx_int+0x158/0x17c)
[<802f88f4>] (imx_int+0x158/0x17c) from [<8007abe0>] (handle_irq_event_percpu+0x50/0x194)
[<8007abe0>] (handle_irq_event_percpu+0x50/0x194) from [<8007ad60>] (handle_irq_event+0x3c/0x5c)
--------------------------------------------------------------------

This patch adds more limits to the @write_wakeup, the one who wants to
implemet the @write_wakeup should follow the limits which avoid the deadlock.

Signed-off-by: Huang Shijie <b32955-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
---
 include/linux/tty_ldisc.h |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index f15c898..539ccc5 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -91,7 +91,10 @@
  *	This function is called by the low-level tty driver to signal
  *	that line discpline should try to send more characters to the
  *	low-level driver for transmission.  If the line discpline does
- *	not have any more data to send, it can just return.
+ *	not have any more data to send, it can just return. If the line
+ *	discipline does have some data to send, please arise a tasklet
+ *	or workqueue to do the real data transfer. Do not send data in
+ *	this hook, it may leads to a deadlock.
  *
  * int (*hangup)(struct tty_struct *)
  *
-- 
1.7.2.rc3

Re: [PATCH RFC] tty_ldisc: add more limits to the @write_wakeup

[Huang Shijie]

于 2013年11月13日 15:30, Huang Shijie 写道:
> In the uart_handle_cts_change(), uart_write_wakeup() is called after
> we call @uart_port->ops->start_tx().
>
> The Documentation/serial/driver tells us:
> -----------------------------------------------
>   start_tx(port)
> 	Start transmitting characters.
>
> 	Locking: port->lock taken.
> 	Interrupts: locally disabled.
> -----------------------------------------------
>
> So when the uart_write_wakeup() is called, the port->lock is taken by
> the upper. See the following callstack:
>
> 	|_ uart_write_wakeup
> 	   |_ tty_wakeup
> 	      |_ ld->ops->write_wakeup
>
> With the port->lock held, we call the @write_wakeup. Some implemetation of
> the @write_wakeup does not notice that the port->lock is held, and it still
> tries to send data with uart_write() which will try to grab the prot->lock.
> A dead lock occurs, see the following log caught in the Bluetooth by uart:
>
> --------------------------------------------------------------------
> BUG: spinlock lockup suspected on CPU#0, swapper/0/0
>  lock: 0xdc3f4410, .magic: dead4ead, .owner: swapper/0/0, .owner_cpu: 0
> CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W    3.10.17-16839-ge4a1bef #1320
> [<80014cbc>] (unwind_backtrace+0x0/0x138) from [<8001251c>] (show_stack+0x10/0x14)
> [<8001251c>] (show_stack+0x10/0x14) from [<802816ac>] (do_raw_spin_lock+0x108/0x184)
> [<802816ac>] (do_raw_spin_lock+0x108/0x184) from [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60)
> [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) from [<802f5754>] (uart_write+0x38/0xe0)
> [<802f5754>] (uart_write+0x38/0xe0) from [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168)
> [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) from [<802dab18>] (tty_wakeup+0x50/0x5c)
> [<802dab18>] (tty_wakeup+0x50/0x5c) from [<802f81a4>] (imx_rtsint+0x50/0x80)
> [<802f81a4>] (imx_rtsint+0x50/0x80) from [<802f88f4>] (imx_int+0x158/0x17c)
> [<802f88f4>] (imx_int+0x158/0x17c) from [<8007abe0>] (handle_irq_event_percpu+0x50/0x194)
> [<8007abe0>] (handle_irq_event_percpu+0x50/0x194) from [<8007ad60>] (handle_irq_event+0x3c/0x5c)
> --------------------------------------------------------------------
>
> This patch adds more limits to the @write_wakeup, the one who wants to
> implemet the @write_wakeup should follow the limits which avoid the deadlock.
>
> Signed-off-by: Huang Shijie <b32955@freescale.com>
> ---
>  include/linux/tty_ldisc.h |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
> index f15c898..539ccc5 100644
> --- a/include/linux/tty_ldisc.h
> +++ b/include/linux/tty_ldisc.h
> @@ -91,7 +91,10 @@
>   *	This function is called by the low-level tty driver to signal
>   *	that line discpline should try to send more characters to the
>   *	low-level driver for transmission.  If the line discpline does
> - *	not have any more data to send, it can just return.
> + *	not have any more data to send, it can just return. If the line
> + *	discipline does have some data to send, please arise a tasklet
> + *	or workqueue to do the real data transfer. Do not send data in
> + *	this hook, it may leads to a deadlock.
>   *
>   * int (*hangup)(struct tty_struct *)
>   *
just a ping.

In actually, this is a BUG in the tty code or BT code.

thanks
Huang Shijie

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Re: [PATCH RFC] tty_ldisc: add more limits to the @write_wakeup

[Peter Hurley]

On 12/06/2013 05:34 AM, Huang Shijie wrote:
> 于 2013年11月13日 15:30, Huang Shijie 写道:
>> In the uart_handle_cts_change(), uart_write_wakeup() is called after
>> we call @uart_port->ops->start_tx().
>>
>> The Documentation/serial/driver tells us:
>> -----------------------------------------------
>>    start_tx(port)
>> 	Start transmitting characters.
>>
>> 	Locking: port->lock taken.
>> 	Interrupts: locally disabled.
>> -----------------------------------------------
>>
>> So when the uart_write_wakeup() is called, the port->lock is taken by
>> the upper. See the following callstack:
>>
>> 	|_ uart_write_wakeup
>> 	   |_ tty_wakeup
>> 	      |_ ld->ops->write_wakeup
>>
>> With the port->lock held, we call the @write_wakeup. Some implemetation of
>> the @write_wakeup does not notice that the port->lock is held, and it still
>> tries to send data with uart_write() which will try to grab the prot->lock.
>> A dead lock occurs, see the following log caught in the Bluetooth by uart:
>>
>> --------------------------------------------------------------------
>> BUG: spinlock lockup suspected on CPU#0, swapper/0/0
>>   lock: 0xdc3f4410, .magic: dead4ead, .owner: swapper/0/0, .owner_cpu: 0
>> CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W    3.10.17-16839-ge4a1bef #1320
>> [<80014cbc>] (unwind_backtrace+0x0/0x138) from [<8001251c>] (show_stack+0x10/0x14)
>> [<8001251c>] (show_stack+0x10/0x14) from [<802816ac>] (do_raw_spin_lock+0x108/0x184)
>> [<802816ac>] (do_raw_spin_lock+0x108/0x184) from [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60)
>> [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) from [<802f5754>] (uart_write+0x38/0xe0)
>> [<802f5754>] (uart_write+0x38/0xe0) from [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168)
>> [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) from [<802dab18>] (tty_wakeup+0x50/0x5c)
>> [<802dab18>] (tty_wakeup+0x50/0x5c) from [<802f81a4>] (imx_rtsint+0x50/0x80)
>> [<802f81a4>] (imx_rtsint+0x50/0x80) from [<802f88f4>] (imx_int+0x158/0x17c)
>> [<802f88f4>] (imx_int+0x158/0x17c) from [<8007abe0>] (handle_irq_event_percpu+0x50/0x194)
>> [<8007abe0>] (handle_irq_event_percpu+0x50/0x194) from [<8007ad60>] (handle_irq_event+0x3c/0x5c)
>> --------------------------------------------------------------------
>>
>> This patch adds more limits to the @write_wakeup, the one who wants to
>> implemet the @write_wakeup should follow the limits which avoid the deadlock.
>>
>> Signed-off-by: Huang Shijie <b32955@freescale.com>
>> ---
>>   include/linux/tty_ldisc.h |    5 ++++-
>>   1 files changed, 4 insertions(+), 1 deletions(-)
>>
>> diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
>> index f15c898..539ccc5 100644
>> --- a/include/linux/tty_ldisc.h
>> +++ b/include/linux/tty_ldisc.h
>> @@ -91,7 +91,10 @@
>>    *	This function is called by the low-level tty driver to signal
>>    *	that line discpline should try to send more characters to the
>>    *	low-level driver for transmission.  If the line discpline does
>> - *	not have any more data to send, it can just return.
>> + *	not have any more data to send, it can just return. If the line
>> + *	discipline does have some data to send, please arise a tasklet
>> + *	or workqueue to do the real data transfer. Do not send data in
>> + *	this hook, it may leads to a deadlock.
>>    *
>>    * int (*hangup)(struct tty_struct *)
>>    *
> just a ping.
>
> In actually, this is a BUG in the tty code or BT code.

hci_uart_tx_wakeup() should perform the actual tx in a work item.

Regards,
Peter Hurley

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Re: [PATCH RFC] tty_ldisc: add more limits to the @write_wakeup

[Huang Shijie]

于 2013年12月07日 00:18, Peter Hurley 写道:
> hci_uart_tx_wakeup() should perform the actual tx in a work item. 
Does the "work item" mean a workqueue or a tasklet?
This patch is used to tell the line discipline writers to send the data 
in the workqueue or a tasklet.

thanks
Huang Shijie

Re: [PATCH RFC] tty_ldisc: add more limits to the @write_wakeup

[Peter Hurley]

On 12/11/2013 01:44 AM, Huang Shijie wrote:
> 于 2013年12月07日 00:18, Peter Hurley 写道:
>> hci_uart_tx_wakeup() should perform the actual tx in a work item.
> Does the "work item" mean a workqueue or a tasklet?
> This patch is used to tell the line discipline writers to send the data in the workqueue or a tasklet.

Yes, "work item" means struct work_struct.

Regards,
Peter Hurley

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