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
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 <[email protected]>
>
>
> > From 3ee6b74833f154df64a6164476b854846206a3f2 Mon Sep 17 00:00:00 2001
> >From: Felipe Balbi <[email protected]>
> >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 <[email protected]>
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 <[email protected]>
> >---
> > 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
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 <[email protected]>
> From 3ee6b74833f154df64a6164476b854846206a3f2 Mon Sep 17 00:00:00 2001
> From: Felipe Balbi <[email protected]>
> 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 <[email protected]>
> Signed-off-by: Felipe Balbi <[email protected]>
> ---
> 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;
>
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 <[email protected]>
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 <[email protected]>
---
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
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 <[email protected]>
> 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 <[email protected]>
> ---
> 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
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 <[email protected]>
>
> Can someone resend it, this is lost in my tree for some reason...
Apologies if my mailer mangles this.
--- >% ---
From: Huang Shijie <[email protected]>
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 <[email protected]>
---
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
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 <[email protected]>
Can someone resend it, this is lost in my tree for some reason...
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 <[email protected]>
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 <[email protected]>
---
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
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;
>
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
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 <[email protected]>
--
balbi
[ +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
[ +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
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
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
.
---Sent from Boxer | http://getboxer.com
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
--
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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