hci_ldsic nested locking problem

hci_ldsic nested locking problem

[Felipe Balbi]

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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() ?

cheers

-- 
balbi

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Re: hci_ldsic nested locking problem

[Alan Cox]

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

Alan

Re: hci_ldsic nested locking problem

[Felipe Balbi]

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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 ?

-- 
balbi

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Re: hci_ldsic nested locking problem

[Felipe Balbi]

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On Thu, Mar 20, 2014 at 12:16:22PM -0500, 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

then we need updates to Documentation:

Documentation/serial/tty.txt::

|  Driver Side Interfaces:
|  
|  receive_buf()	-	Hand buffers of bytes from the driver to the ldisc
|  			for processing. Semantics currently rather
|  			mysterious 8(
|  
|  write_wakeup()	-	May be called at any point between open and close.
|  			The TTY_DO_WRITE_WAKEUP flag indicates if a call
|  			is needed but always races versus calls. Thus the
|  			ldisc must be careful about setting order and to
|  			handle unexpected calls. Must not sleep.
|  
|  			The driver is forbidden from calling this directly
|  			from the ->write call from the ldisc as the ldisc
|  			is permitted to call the driver write method from
|  			this function. In such a situation defer it.

documentation says ldisc is allowed to call ->write() from
->write_wakeup(). huh ?

-- 
balbi

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Re: hci_ldsic nested locking problem

[Peter Hurley]

[ +cc Huang Shijie ]

On 03/20/2014 01:29 PM, Felipe Balbi wrote:
> then we need updates to Documentation:
>
> Documentation/serial/tty.txt::
>
> |  Driver Side Interfaces:
> |
> |  receive_buf()	-	Hand buffers of bytes from the driver to the ldisc
> |  			for processing. Semantics currently rather
> |  			mysterious 8(
> |
> |  write_wakeup()	-	May be called at any point between open and close.
> |  			The TTY_DO_WRITE_WAKEUP flag indicates if a call
> |  			is needed but always races versus calls. Thus the
> |  			ldisc must be careful about setting order and to
> |  			handle unexpected calls. Must not sleep.
> |
> |  			The driver is forbidden from calling this directly
> |  			from the ->write call from the ldisc as the ldisc
> |  			is permitted to call the driver write method from
> |  			this function. In such a situation defer it.
>
> documentation says ldisc is allowed to call ->write() from
> ->write_wakeup(). huh ?

Patch submitted but never applied.

http://www.spinics.net/lists/linux-serial/msg11144.html

Regards,
Peter Hurley

Re: hci_ldsic nested locking problem

[Felipe Balbi]

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On Thu, Mar 20, 2014 at 01:34:57PM -0400, Peter Hurley wrote:
> [ +cc Huang Shijie ]
> 
> On 03/20/2014 01:29 PM, Felipe Balbi wrote:
> >then we need updates to Documentation:
> >
> >Documentation/serial/tty.txt::
> >
> >|  Driver Side Interfaces:
> >|
> >|  receive_buf()	-	Hand buffers of bytes from the driver to the ldisc
> >|  			for processing. Semantics currently rather
> >|  			mysterious 8(
> >|
> >|  write_wakeup()	-	May be called at any point between open and close.
> >|  			The TTY_DO_WRITE_WAKEUP flag indicates if a call
> >|  			is needed but always races versus calls. Thus the
> >|  			ldisc must be careful about setting order and to
> >|  			handle unexpected calls. Must not sleep.
> >|
> >|  			The driver is forbidden from calling this directly
> >|  			from the ->write call from the ldisc as the ldisc
> >|  			is permitted to call the driver write method from
> >|  			this function. In such a situation defer it.
> >
> >documentation says ldisc is allowed to call ->write() from
> >->write_wakeup(). huh ?
> 
> Patch submitted but never applied.
> 
> http://www.spinics.net/lists/linux-serial/msg11144.html

Thank you. For that patch:

Acked-by: Felipe Balbi <balbi@ti.com>

-- 
balbi

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Re: hci_ldsic nested locking problem

[Greg KH]

On Thu, Mar 20, 2014 at 12:35:18PM -0500, Felipe Balbi wrote:
> On Thu, Mar 20, 2014 at 01:34:57PM -0400, Peter Hurley wrote:
> > [ +cc Huang Shijie ]
> > 
> > On 03/20/2014 01:29 PM, Felipe Balbi wrote:
> > >then we need updates to Documentation:
> > >
> > >Documentation/serial/tty.txt::
> > >
> > >|  Driver Side Interfaces:
> > >|
> > >|  receive_buf()	-	Hand buffers of bytes from the driver to the ldisc
> > >|  			for processing. Semantics currently rather
> > >|  			mysterious 8(
> > >|
> > >|  write_wakeup()	-	May be called at any point between open and close.
> > >|  			The TTY_DO_WRITE_WAKEUP flag indicates if a call
> > >|  			is needed but always races versus calls. Thus the
> > >|  			ldisc must be careful about setting order and to
> > >|  			handle unexpected calls. Must not sleep.
> > >|
> > >|  			The driver is forbidden from calling this directly
> > >|  			from the ->write call from the ldisc as the ldisc
> > >|  			is permitted to call the driver write method from
> > >|  			this function. In such a situation defer it.
> > >
> > >documentation says ldisc is allowed to call ->write() from
> > >->write_wakeup(). huh ?
> > 
> > Patch submitted but never applied.
> > 
> > http://www.spinics.net/lists/linux-serial/msg11144.html
> 
> Thank you. For that patch:
> 
> Acked-by: Felipe Balbi <balbi@ti.com>

Can someone resend it, this is lost in my tree for some reason...

Re: hci_ldsic nested locking problem

[Peter Hurley]

On 03/20/2014 02:45 PM, Greg KH wrote:
> On Thu, Mar 20, 2014 at 12:35:18PM -0500, Felipe Balbi wrote:
>> On Thu, Mar 20, 2014 at 01:34:57PM -0400, Peter Hurley wrote:
>>> [ +cc Huang Shijie ]
>>>
>>> On 03/20/2014 01:29 PM, Felipe Balbi wrote:
>>>> then we need updates to Documentation:
>>>>
>>>> Documentation/serial/tty.txt::
>>>>
>>>> |  Driver Side Interfaces:
>>>> |
>>>> |  receive_buf()	-	Hand buffers of bytes from the driver to the ldisc
>>>> |  			for processing. Semantics currently rather
>>>> |  			mysterious 8(
>>>> |
>>>> |  write_wakeup()	-	May be called at any point between open and close.
>>>> |  			The TTY_DO_WRITE_WAKEUP flag indicates if a call
>>>> |  			is needed but always races versus calls. Thus the
>>>> |  			ldisc must be careful about setting order and to
>>>> |  			handle unexpected calls. Must not sleep.
>>>> |
>>>> |  			The driver is forbidden from calling this directly
>>>> |  			from the ->write call from the ldisc as the ldisc
>>>> |  			is permitted to call the driver write method from
>>>> |  			this function. In such a situation defer it.
>>>>
>>>> documentation says ldisc is allowed to call ->write() from
>>>> ->write_wakeup(). huh ?
>>>
>>> Patch submitted but never applied.
>>>
>>> http://www.spinics.net/lists/linux-serial/msg11144.html
>>
>> Thank you. For that patch:
>>
>> Acked-by: Felipe Balbi <balbi@ti.com>
>
> Can someone resend it, this is lost in my tree for some reason...

Apologies if my mailer mangles this.

--- >% ---
From: Huang Shijie <b32955@freescale.com>

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 *)
   *
-- 1.7.2.rc3

Re: hci_ldsic nested locking problem

[Peter Hurley]

[ +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.

Regards,
Peter Hurley

Re: hci_ldsic nested locking problem

[Felipe Balbi]

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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:

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;

-- 
balbi

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Re: hci_ldsic nested locking problem

[Peter Hurley]

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;
>

Re: hci_ldsic nested locking problem

[Felipe Balbi]

[-- Attachment #1: Type: text/plain, Size: 4486 bytes --]

On Thu, Mar 20, 2014 at 02:21:17PM -0400, Peter Hurley wrote:
> 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?

here, as a patch too this time:

From 3ee6b74833f154df64a6164476b854846206a3f2 Mon Sep 17 00:00:00 2001
From: Felipe Balbi <balbi@ti.com>
Date: Thu, 20 Mar 2014 13:20:10 -0500
Subject: [PATCH] bluetooth: hci_ldisc: fix deadlock condition

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.

Signed-off-by: Felipe Balbi <balbi@ti.com>
---
 drivers/bluetooth/hci_ldisc.c | 20 +++++++++++++++-----
 drivers/bluetooth/hci_uart.h  |  1 +
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 6e06f6f..ecdd765 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)
@@ -281,6 +288,7 @@ 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 +326,8 @@ static void hci_uart_tty_close(struct tty_struct *tty)
 	if (hdev)
 		hci_uart_close(hdev);
 
+	cancel_work_sync(&hy->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;
-- 
1.9.1.286.g5172cb3


-- 
balbi

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]

Re: hci_ldsic nested locking problem

[Felipe Balbi]

[-- Attachment #1: Type: text/plain, Size: 4289 bytes --]

On Thu, Mar 20, 2014 at 01:25:28PM -0500, Felipe Balbi wrote:
> On Thu, Mar 20, 2014 at 02:21:17PM -0400, Peter Hurley wrote:
> > 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?
> 
> here, as a patch too this time:
> 
> From 3ee6b74833f154df64a6164476b854846206a3f2 Mon Sep 17 00:00:00 2001
> From: Felipe Balbi <balbi@ti.com>
> Date: Thu, 20 Mar 2014 13:20:10 -0500
> Subject: [PATCH] bluetooth: hci_ldisc: fix deadlock condition
> 
> 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.
> 
> Signed-off-by: Felipe Balbi <balbi@ti.com>
> ---
>  drivers/bluetooth/hci_ldisc.c | 20 +++++++++++++++-----
>  drivers/bluetooth/hci_uart.h  |  1 +
>  2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index 6e06f6f..ecdd765 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)
> @@ -281,6 +288,7 @@ 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 +326,8 @@ static void hci_uart_tty_close(struct tty_struct *tty)
>  	if (hdev)
>  		hci_uart_close(hdev);
>  
> +	cancel_work_sync(&hy->write_work);

forgot to commit, darn it

-- 
balbi

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]

Re: hci_ldsic nested locking problem

[Felipe Balbi]

[-- Attachment #1: Type: text/plain, Size: 3047 bytes --]

Hi,

On Thu, Mar 20, 2014 at 02:01:54PM -0500, Felipe Balbi wrote:
> > @@ -318,6 +326,8 @@ static void hci_uart_tty_close(struct tty_struct *tty)
> >  	if (hdev)
> >  		hci_uart_close(hdev);
> >  
> > +	cancel_work_sync(&hy->write_work);
> 
> forgot to commit, darn it

here it is:

From eaf7ff6f2d224f202369e4820b76a03fa664fab0 Mon Sep 17 00:00:00 2001
From: Felipe Balbi <balbi@ti.com>
Date: Thu, 20 Mar 2014 13:20:10 -0500
Subject: [PATCH] bluetooth: hci_ldisc: fix deadlock condition

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.

Signed-off-by: Felipe Balbi <balbi@ti.com>
---
 drivers/bluetooth/hci_ldisc.c | 20 +++++++++++++++-----
 drivers/bluetooth/hci_uart.h  |  1 +
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 6e06f6f..5a53e50 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)
@@ -281,6 +288,7 @@ 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 +326,8 @@ 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;
-- 
1.9.1.286.g5172cb3


-- 
balbi

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]

Re: hci_ldsic nested locking problem

[Peter Hurley]

On 03/20/2014 02:25 PM, Felipe Balbi wrote:
> On Thu, Mar 20, 2014 at 02:21:17PM -0400, Peter Hurley wrote:
>> 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?
>
> here, as a patch too this time:

Thanks. Minor edits below but, strictly speaking, not necessary.

Reviewed-by: Peter Hurley <peter@hurleysoftware.com>


>  From 3ee6b74833f154df64a6164476b854846206a3f2 Mon Sep 17 00:00:00 2001
> From: Felipe Balbi <balbi@ti.com>
> Date: Thu, 20 Mar 2014 13:20:10 -0500
> Subject: [PATCH] bluetooth: hci_ldisc: fix deadlock condition
>
> 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 know you found it independently but ?

Reported-by: Huang Shijie <b32955@freescale.com>

> Signed-off-by: Felipe Balbi <balbi@ti.com>
> ---
>   drivers/bluetooth/hci_ldisc.c | 20 +++++++++++++++-----
>   drivers/bluetooth/hci_uart.h  |  1 +
>   2 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index 6e06f6f..ecdd765 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;
> +

+	/* FIXME: if bad skb length or tty->ops->write() returns < 0 ??? */

>   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)
> @@ -281,6 +288,7 @@ 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 +326,8 @@ static void hci_uart_tty_close(struct tty_struct *tty)
>   	if (hdev)
>   		hci_uart_close(hdev);
>
> +	cancel_work_sync(&hy->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;
>

Re: hci_ldsic nested locking problem

[Felipe Balbi]

[-- Attachment #1: Type: text/plain, Size: 5439 bytes --]

Hi,

On Thu, Mar 20, 2014 at 03:16:35PM -0400, Peter Hurley wrote:
> On 03/20/2014 02:25 PM, Felipe Balbi wrote:
> >On Thu, Mar 20, 2014 at 02:21:17PM -0400, Peter Hurley wrote:
> >>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?
> >
> >here, as a patch too this time:
> 
> Thanks. Minor edits below but, strictly speaking, not necessary.
> 
> Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
> 
> 
> > From 3ee6b74833f154df64a6164476b854846206a3f2 Mon Sep 17 00:00:00 2001
> >From: Felipe Balbi <balbi@ti.com>
> >Date: Thu, 20 Mar 2014 13:20:10 -0500
> >Subject: [PATCH] bluetooth: hci_ldisc: fix deadlock condition
> >
> >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 know you found it independently but ?
> 
> Reported-by: Huang Shijie <b32955@freescale.com>

I will never add any *-by tags without seeing it in the mailing list.
Now I can add it to the patch and send it as a real patch (git
send-email it).

> >Signed-off-by: Felipe Balbi <balbi@ti.com>
> >---
> >  drivers/bluetooth/hci_ldisc.c | 20 +++++++++++++++-----
> >  drivers/bluetooth/hci_uart.h  |  1 +
> >  2 files changed, 16 insertions(+), 5 deletions(-)
> >
> >diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> >index 6e06f6f..ecdd765 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;
> >+
> 
> +	/* FIXME: if bad skb length or tty->ops->write() returns < 0 ??? */
> 
> >  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)
> >@@ -281,6 +288,7 @@ 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 +326,8 @@ static void hci_uart_tty_close(struct tty_struct *tty)
> >  	if (hdev)
> >  		hci_uart_close(hdev);
> >
> >+	cancel_work_sync(&hy->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;
> >
> 

-- 
balbi

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