[PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[cschneider]

From: Christian Schneider <christian@ch-sc.de>

sysfs_notify and kobject_uevent are passed the wrong kobject.
that why notifications can't be received and uevents have the wrong path.
this patch fixes this.

Signed-off-by: Christian Schneider <cschneider@radiodata.biz>
---
 drivers/hwmon/gpio-fan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
index 84753680a4e8..76377791ff0e 100644
--- a/drivers/hwmon/gpio-fan.c
+++ b/drivers/hwmon/gpio-fan.c
@@ -54,8 +54,8 @@ static void fan_alarm_notify(struct work_struct *ws)
 	struct gpio_fan_data *fan_data =
 		container_of(ws, struct gpio_fan_data, alarm_work);
 
-	sysfs_notify(&fan_data->dev->kobj, NULL, "fan1_alarm");
-	kobject_uevent(&fan_data->dev->kobj, KOBJ_CHANGE);
+	sysfs_notify(&fan_data->hwmon_dev->kobj, NULL, "fan1_alarm");
+	kobject_uevent(&fan_data->hwmon_dev->kobj, KOBJ_CHANGE);
 }
 
 static irqreturn_t fan_alarm_irq_handler(int irq, void *dev_id)
-- 
2.17.1

Re: [PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[Guenter Roeck]

On Mon, Jun 17, 2019 at 11:33:43AM +0200, cschneider@radiodata.biz wrote:
> From: Christian Schneider <christian@ch-sc.de>
> 
> sysfs_notify and kobject_uevent are passed the wrong kobject.
> that why notifications can't be received and uevents have the wrong path.
> this patch fixes this.
> 
> Signed-off-by: Christian Schneider <cschneider@radiodata.biz>

Applied.

In the future, please version your patches, add a change log,
and reflect the subsystem and driver in the subject line.

Thanks,
Guenter

> ---
>  drivers/hwmon/gpio-fan.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
> index 84753680a4e8..76377791ff0e 100644
> --- a/drivers/hwmon/gpio-fan.c
> +++ b/drivers/hwmon/gpio-fan.c
> @@ -54,8 +54,8 @@ static void fan_alarm_notify(struct work_struct *ws)
>  	struct gpio_fan_data *fan_data =
>  		container_of(ws, struct gpio_fan_data, alarm_work);
>  
> -	sysfs_notify(&fan_data->dev->kobj, NULL, "fan1_alarm");
> -	kobject_uevent(&fan_data->dev->kobj, KOBJ_CHANGE);
> +	sysfs_notify(&fan_data->hwmon_dev->kobj, NULL, "fan1_alarm");
> +	kobject_uevent(&fan_data->hwmon_dev->kobj, KOBJ_CHANGE);
>  }
>  
>  static irqreturn_t fan_alarm_irq_handler(int irq, void *dev_id)

Re: [PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[Christian Schneider]

Hi,
unfrotunately I found a problem with my patch. It didn't appear on the 
devices, where I tested, only when distributing the patch to more 
devices, it occurs sometimes.

There is a possible race condition. In gpio_fan_probe, the IRQ handler 
for the fan alarm is registered before the hwmon_dev is initialised.
So it is possible, that the handler executes, while fandata->hwmon_dev 
is still unitialised and the handler runs in an invalid pointer dereference.

The obvious fix, moving the
/* Configure alarm GPIO if available. */
if (fan_data->alarm_gpio) {
	err = fan_alarm_init(fan_data);
	if (err)
		return err;
}
block after

/* Make this driver part of hwmon class. */
fan_data->hwmon_dev =
	devm_hwmon_device_register_with_groups(dev,
					       "gpio_fan", fan_data,
					       gpio_fan_groups);

doesn't work. Sysfs doesn't have a fan1_alarm attribute anymore then.

It is not yet clear to me, why creation of the attribute fails in this 
case. I need to investigate further.
In the meanwhile, please revert my patch.

I'm sorry for the disturbance I created....

BR, Christian


Am 17.06.2019 um 18:04 schrieb Guenter Roeck:
> On Mon, Jun 17, 2019 at 11:33:43AM +0200, cschneider@radiodata.biz wrote:
>> From: Christian Schneider <christian@ch-sc.de>
>>
>> sysfs_notify and kobject_uevent are passed the wrong kobject.
>> that why notifications can't be received and uevents have the wrong path.
>> this patch fixes this.
>>
>> Signed-off-by: Christian Schneider <cschneider@radiodata.biz>
> 
> Applied.
> 
> In the future, please version your patches, add a change log,
> and reflect the subsystem and driver in the subject line.
> 
> Thanks,
> Guenter
> 
>> ---
>>   drivers/hwmon/gpio-fan.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
>> index 84753680a4e8..76377791ff0e 100644
>> --- a/drivers/hwmon/gpio-fan.c
>> +++ b/drivers/hwmon/gpio-fan.c
>> @@ -54,8 +54,8 @@ static void fan_alarm_notify(struct work_struct *ws)
>>   	struct gpio_fan_data *fan_data =
>>   		container_of(ws, struct gpio_fan_data, alarm_work);
>>   
>> -	sysfs_notify(&fan_data->dev->kobj, NULL, "fan1_alarm");
>> -	kobject_uevent(&fan_data->dev->kobj, KOBJ_CHANGE);
>> +	sysfs_notify(&fan_data->hwmon_dev->kobj, NULL, "fan1_alarm");
>> +	kobject_uevent(&fan_data->hwmon_dev->kobj, KOBJ_CHANGE);
>>   }
>>   
>>   static irqreturn_t fan_alarm_irq_handler(int irq, void *dev_id)

Re: [PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[Christian Schneider]

Ok, seems that moving that block, where fan_alarm_init is called down, 
isn't a problem on master.
I need to use 4.9, cause we have an embedded device that needs patches, 
and they are only available for older kernels.

In 4.9, fan_alarm_init() does fan_data->alarm = alarm;
When fan_alarm_init() is called after 
devm_hwmon_device_register_with_groups(), then fan_data->alarm is not 
yet set, so the sysfs attribute is not created.

when I move the fan_data->alarm = alarm; out of fan_alarm_init() before 
devm_hwmon_device_register_with_groups() and the fan_alarm_init() after, 
then it works, and doesn't have a race condition.

On master, populating fan_data->alarm_gpio is done in 
gpio_fan_get_of_data(fan_data); as far as I understand, so moving the 
fan_alarm_init() block further down shouldn't be a problem.

I don't know, how I can test this with master kernel. Unfortunately, the 
device, I'm using doesn't have a recent kernel. And on my normal 
(desktop) pc, I don't have a gpio fan.
How should I proceed now?


BR, Christian

Am 19.06.2019 um 09:47 schrieb Christian Schneider:
> Hi,
> unfrotunately I found a problem with my patch. It didn't appear on the 
> devices, where I tested, only when distributing the patch to more 
> devices, it occurs sometimes.
> 
> There is a possible race condition. In gpio_fan_probe, the IRQ handler 
> for the fan alarm is registered before the hwmon_dev is initialised.
> So it is possible, that the handler executes, while fandata->hwmon_dev 
> is still unitialised and the handler runs in an invalid pointer 
> dereference.
> 
> The obvious fix, moving the
> /* Configure alarm GPIO if available. */
> if (fan_data->alarm_gpio) {
>      err = fan_alarm_init(fan_data);
>      if (err)
>          return err;
> }
> block after
> 
> /* Make this driver part of hwmon class. */
> fan_data->hwmon_dev =
>      devm_hwmon_device_register_with_groups(dev,
>                             "gpio_fan", fan_data,
>                             gpio_fan_groups);
> 
> doesn't work. Sysfs doesn't have a fan1_alarm attribute anymore then.
> 
> It is not yet clear to me, why creation of the attribute fails in this 
> case. I need to investigate further.
> In the meanwhile, please revert my patch.
> 
> I'm sorry for the disturbance I created....
> 
> BR, Christian
> 
> 
> Am 17.06.2019 um 18:04 schrieb Guenter Roeck:
>> On Mon, Jun 17, 2019 at 11:33:43AM +0200, cschneider@radiodata.biz wrote:
>>> From: Christian Schneider <christian@ch-sc.de>
>>>
>>> sysfs_notify and kobject_uevent are passed the wrong kobject.
>>> that why notifications can't be received and uevents have the wrong 
>>> path.
>>> this patch fixes this.
>>>
>>> Signed-off-by: Christian Schneider <cschneider@radiodata.biz>
>>
>> Applied.
>>
>> In the future, please version your patches, add a change log,
>> and reflect the subsystem and driver in the subject line.
>>
>> Thanks,
>> Guenter
>>
>>> ---
>>>   drivers/hwmon/gpio-fan.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
>>> index 84753680a4e8..76377791ff0e 100644
>>> --- a/drivers/hwmon/gpio-fan.c
>>> +++ b/drivers/hwmon/gpio-fan.c
>>> @@ -54,8 +54,8 @@ static void fan_alarm_notify(struct work_struct *ws)
>>>       struct gpio_fan_data *fan_data =
>>>           container_of(ws, struct gpio_fan_data, alarm_work);
>>> -    sysfs_notify(&fan_data->dev->kobj, NULL, "fan1_alarm");
>>> -    kobject_uevent(&fan_data->dev->kobj, KOBJ_CHANGE);
>>> +    sysfs_notify(&fan_data->hwmon_dev->kobj, NULL, "fan1_alarm");
>>> +    kobject_uevent(&fan_data->hwmon_dev->kobj, KOBJ_CHANGE);
>>>   }
>>>   static irqreturn_t fan_alarm_irq_handler(int irq, void *dev_id)

Re: [PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[Guenter Roeck]

On Wed, Jun 19, 2019 at 12:00:37PM +0200, Christian Schneider wrote:
> Ok, seems that moving that block, where fan_alarm_init is called down, isn't
> a problem on master.
> I need to use 4.9, cause we have an embedded device that needs patches, and
> they are only available for older kernels.
> 
> In 4.9, fan_alarm_init() does fan_data->alarm = alarm;
> When fan_alarm_init() is called after
> devm_hwmon_device_register_with_groups(), then fan_data->alarm is not yet
> set, so the sysfs attribute is not created.
> 
> when I move the fan_data->alarm = alarm; out of fan_alarm_init() before
> devm_hwmon_device_register_with_groups() and the fan_alarm_init() after,
> then it works, and doesn't have a race condition.
> 
> On master, populating fan_data->alarm_gpio is done in
> gpio_fan_get_of_data(fan_data); as far as I understand, so moving the
> fan_alarm_init() block further down shouldn't be a problem.
> 
> I don't know, how I can test this with master kernel. Unfortunately, the
> device, I'm using doesn't have a recent kernel. And on my normal (desktop)
> pc, I don't have a gpio fan.
> How should I proceed now?
> 

Essentially, we'll need two patches: One to move fan_alarm_init() after
devm_hwmon_device_register_with_groups(), and then the notification patch.
For the backport to v4.9, the first patch will have to be slightly modified:
The first part will a simple
	fan_data->alarm = pdata->alarm;
at the location where fan_alarm_init() is called now, the second part is to move
the call to fan_alarm_init() after devm_hwmon_device_register_with_groups().

It is ok to test the result with your 4.9 based kernel; we'll just have to be
careful when reviewing the mainline patch.

Thanks,
Guenter

> 
> BR, Christian
> 
> Am 19.06.2019 um 09:47 schrieb Christian Schneider:
> >Hi,
> >unfrotunately I found a problem with my patch. It didn't appear on the
> >devices, where I tested, only when distributing the patch to more devices,
> >it occurs sometimes.
> >
> >There is a possible race condition. In gpio_fan_probe, the IRQ handler for
> >the fan alarm is registered before the hwmon_dev is initialised.
> >So it is possible, that the handler executes, while fandata->hwmon_dev is
> >still unitialised and the handler runs in an invalid pointer dereference.
> >
> >The obvious fix, moving the
> >/* Configure alarm GPIO if available. */
> >if (fan_data->alarm_gpio) {
> >     err = fan_alarm_init(fan_data);
> >     if (err)
> >         return err;
> >}
> >block after
> >
> >/* Make this driver part of hwmon class. */
> >fan_data->hwmon_dev =
> >     devm_hwmon_device_register_with_groups(dev,
> >                            "gpio_fan", fan_data,
> >                            gpio_fan_groups);
> >
> >doesn't work. Sysfs doesn't have a fan1_alarm attribute anymore then.
> >
> >It is not yet clear to me, why creation of the attribute fails in this
> >case. I need to investigate further.
> >In the meanwhile, please revert my patch.
> >
> >I'm sorry for the disturbance I created....
> >
> >BR, Christian
> >
> >
> >Am 17.06.2019 um 18:04 schrieb Guenter Roeck:
> >>On Mon, Jun 17, 2019 at 11:33:43AM +0200, cschneider@radiodata.biz wrote:
> >>>From: Christian Schneider <christian@ch-sc.de>
> >>>
> >>>sysfs_notify and kobject_uevent are passed the wrong kobject.
> >>>that why notifications can't be received and uevents have the wrong
> >>>path.
> >>>this patch fixes this.
> >>>
> >>>Signed-off-by: Christian Schneider <cschneider@radiodata.biz>
> >>
> >>Applied.
> >>
> >>In the future, please version your patches, add a change log,
> >>and reflect the subsystem and driver in the subject line.
> >>
> >>Thanks,
> >>Guenter
> >>
> >>>---
> >>>  drivers/hwmon/gpio-fan.c | 4 ++--
> >>>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>>diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
> >>>index 84753680a4e8..76377791ff0e 100644
> >>>--- a/drivers/hwmon/gpio-fan.c
> >>>+++ b/drivers/hwmon/gpio-fan.c
> >>>@@ -54,8 +54,8 @@ static void fan_alarm_notify(struct work_struct *ws)
> >>>      struct gpio_fan_data *fan_data =
> >>>          container_of(ws, struct gpio_fan_data, alarm_work);
> >>>-    sysfs_notify(&fan_data->dev->kobj, NULL, "fan1_alarm");
> >>>-    kobject_uevent(&fan_data->dev->kobj, KOBJ_CHANGE);
> >>>+    sysfs_notify(&fan_data->hwmon_dev->kobj, NULL, "fan1_alarm");
> >>>+    kobject_uevent(&fan_data->hwmon_dev->kobj, KOBJ_CHANGE);
> >>>  }
> >>>  static irqreturn_t fan_alarm_irq_handler(int irq, void *dev_id)

Re: [PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[Guenter Roeck]

On Wed, Jun 19, 2019 at 10:47:34AM +0200, Christian Schneider wrote:
> Hi,
> unfrotunately I found a problem with my patch. It didn't appear on the
> devices, where I tested, only when distributing the patch to more devices,
> it occurs sometimes.
> 
> There is a possible race condition. In gpio_fan_probe, the IRQ handler for
> the fan alarm is registered before the hwmon_dev is initialised.
> So it is possible, that the handler executes, while fandata->hwmon_dev is
> still unitialised and the handler runs in an invalid pointer dereference.
> 
> The obvious fix, moving the
> /* Configure alarm GPIO if available. */
> if (fan_data->alarm_gpio) {
> 	err = fan_alarm_init(fan_data);
> 	if (err)
> 		return err;
> }
> block after
> 
> /* Make this driver part of hwmon class. */
> fan_data->hwmon_dev =
> 	devm_hwmon_device_register_with_groups(dev,
> 					       "gpio_fan", fan_data,
> 					       gpio_fan_groups);
> 
> doesn't work. Sysfs doesn't have a fan1_alarm attribute anymore then.
> 
> It is not yet clear to me, why creation of the attribute fails in this case.
> I need to investigate further.
> In the meanwhile, please revert my patch.
> 
> I'm sorry for the disturbance I created....
> 
No worries. Thanks for noticing and for reporting the problem. I dropped
the patch from the queue for now.

Guenter

> BR, Christian
> 
> 
> Am 17.06.2019 um 18:04 schrieb Guenter Roeck:
> >On Mon, Jun 17, 2019 at 11:33:43AM +0200, cschneider@radiodata.biz wrote:
> >>From: Christian Schneider <christian@ch-sc.de>
> >>
> >>sysfs_notify and kobject_uevent are passed the wrong kobject.
> >>that why notifications can't be received and uevents have the wrong path.
> >>this patch fixes this.
> >>
> >>Signed-off-by: Christian Schneider <cschneider@radiodata.biz>
> >
> >Applied.
> >
> >In the future, please version your patches, add a change log,
> >and reflect the subsystem and driver in the subject line.
> >
> >Thanks,
> >Guenter
> >
> >>---
> >>  drivers/hwmon/gpio-fan.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >>diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
> >>index 84753680a4e8..76377791ff0e 100644
> >>--- a/drivers/hwmon/gpio-fan.c
> >>+++ b/drivers/hwmon/gpio-fan.c
> >>@@ -54,8 +54,8 @@ static void fan_alarm_notify(struct work_struct *ws)
> >>  	struct gpio_fan_data *fan_data =
> >>  		container_of(ws, struct gpio_fan_data, alarm_work);
> >>-	sysfs_notify(&fan_data->dev->kobj, NULL, "fan1_alarm");
> >>-	kobject_uevent(&fan_data->dev->kobj, KOBJ_CHANGE);
> >>+	sysfs_notify(&fan_data->hwmon_dev->kobj, NULL, "fan1_alarm");
> >>+	kobject_uevent(&fan_data->hwmon_dev->kobj, KOBJ_CHANGE);
> >>  }
> >>  static irqreturn_t fan_alarm_irq_handler(int irq, void *dev_id)

Re: [PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[Christian Schneider]

Am 19.06.2019 um 20:53 schrieb Guenter Roeck:
> On Wed, Jun 19, 2019 at 12:00:37PM +0200, Christian Schneider wrote:
>> Ok, seems that moving that block, where fan_alarm_init is called down, isn't
>> a problem on master.
>> I need to use 4.9, cause we have an embedded device that needs patches, and
>> they are only available for older kernels.
>>
>> In 4.9, fan_alarm_init() does fan_data->alarm = alarm;
>> When fan_alarm_init() is called after
>> devm_hwmon_device_register_with_groups(), then fan_data->alarm is not yet
>> set, so the sysfs attribute is not created.
>>
>> when I move the fan_data->alarm = alarm; out of fan_alarm_init() before
>> devm_hwmon_device_register_with_groups() and the fan_alarm_init() after,
>> then it works, and doesn't have a race condition.
>>
>> On master, populating fan_data->alarm_gpio is done in
>> gpio_fan_get_of_data(fan_data); as far as I understand, so moving the
>> fan_alarm_init() block further down shouldn't be a problem.
>>
>> I don't know, how I can test this with master kernel. Unfortunately, the
>> device, I'm using doesn't have a recent kernel. And on my normal (desktop)
>> pc, I don't have a gpio fan.
>> How should I proceed now?
>>
> 
> Essentially, we'll need two patches: One to move fan_alarm_init() after
> devm_hwmon_device_register_with_groups(), and then the notification patch.
> For the backport to v4.9, the first patch will have to be slightly modified:
> The first part will a simple
> 	fan_data->alarm = pdata->alarm;
> at the location where fan_alarm_init() is called now, the second part is to move
> the call to fan_alarm_init() after devm_hwmon_device_register_with_groups().
> 
> It is ok to test the result with your 4.9 based kernel; we'll just have to be
> careful when reviewing the mainline patch.
> 
> Thanks,
> Guenter

Ok,
it seems like it is working as expected now on my 4.9 kernel. No 
race-condition and notification is received.
I will adopt the changes to mainline kernel, but not sure if I can make 
it today. Might be Monday, till I have the patch.

BR, Christian

> 
>>
>> BR, Christian
>>
>> Am 19.06.2019 um 09:47 schrieb Christian Schneider:
>>> Hi,
>>> unfrotunately I found a problem with my patch. It didn't appear on the
>>> devices, where I tested, only when distributing the patch to more devices,
>>> it occurs sometimes.
>>>
>>> There is a possible race condition. In gpio_fan_probe, the IRQ handler for
>>> the fan alarm is registered before the hwmon_dev is initialised.
>>> So it is possible, that the handler executes, while fandata->hwmon_dev is
>>> still unitialised and the handler runs in an invalid pointer dereference.
>>>
>>> The obvious fix, moving the
>>> /* Configure alarm GPIO if available. */
>>> if (fan_data->alarm_gpio) {
>>>      err = fan_alarm_init(fan_data);
>>>      if (err)
>>>          return err;
>>> }
>>> block after
>>>
>>> /* Make this driver part of hwmon class. */
>>> fan_data->hwmon_dev =
>>>      devm_hwmon_device_register_with_groups(dev,
>>>                             "gpio_fan", fan_data,
>>>                             gpio_fan_groups);
>>>
>>> doesn't work. Sysfs doesn't have a fan1_alarm attribute anymore then.
>>>
>>> It is not yet clear to me, why creation of the attribute fails in this
>>> case. I need to investigate further.
>>> In the meanwhile, please revert my patch.
>>>
>>> I'm sorry for the disturbance I created....
>>>
>>> BR, Christian
>>>
>>>
>>> Am 17.06.2019 um 18:04 schrieb Guenter Roeck:
>>>> On Mon, Jun 17, 2019 at 11:33:43AM +0200, cschneider@radiodata.biz wrote:
>>>>> From: Christian Schneider <christian@ch-sc.de>
>>>>>
>>>>> sysfs_notify and kobject_uevent are passed the wrong kobject.
>>>>> that why notifications can't be received and uevents have the wrong
>>>>> path.
>>>>> this patch fixes this.
>>>>>
>>>>> Signed-off-by: Christian Schneider <cschneider@radiodata.biz>
>>>>
>>>> Applied.
>>>>
>>>> In the future, please version your patches, add a change log,
>>>> and reflect the subsystem and driver in the subject line.
>>>>
>>>> Thanks,
>>>> Guenter
>>>>
>>>>> ---
>>>>>    drivers/hwmon/gpio-fan.c | 4 ++--
>>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
>>>>> index 84753680a4e8..76377791ff0e 100644
>>>>> --- a/drivers/hwmon/gpio-fan.c
>>>>> +++ b/drivers/hwmon/gpio-fan.c
>>>>> @@ -54,8 +54,8 @@ static void fan_alarm_notify(struct work_struct *ws)
>>>>>        struct gpio_fan_data *fan_data =
>>>>>            container_of(ws, struct gpio_fan_data, alarm_work);
>>>>> -    sysfs_notify(&fan_data->dev->kobj, NULL, "fan1_alarm");
>>>>> -    kobject_uevent(&fan_data->dev->kobj, KOBJ_CHANGE);
>>>>> +    sysfs_notify(&fan_data->hwmon_dev->kobj, NULL, "fan1_alarm");
>>>>> +    kobject_uevent(&fan_data->hwmon_dev->kobj, KOBJ_CHANGE);
>>>>>    }
>>>>>    static irqreturn_t fan_alarm_irq_handler(int irq, void *dev_id)

Re: [PATCH] Fix sysfs_notify and kobject_uevent in fan_alarm_notify

[Guenter Roeck]

On 6/21/19 1:30 AM, Christian Schneider wrote:
> Am 19.06.2019 um 20:53 schrieb Guenter Roeck:
>> On Wed, Jun 19, 2019 at 12:00:37PM +0200, Christian Schneider wrote:
>>> Ok, seems that moving that block, where fan_alarm_init is called down, isn't
>>> a problem on master.
>>> I need to use 4.9, cause we have an embedded device that needs patches, and
>>> they are only available for older kernels.
>>>
>>> In 4.9, fan_alarm_init() does fan_data->alarm = alarm;
>>> When fan_alarm_init() is called after
>>> devm_hwmon_device_register_with_groups(), then fan_data->alarm is not yet
>>> set, so the sysfs attribute is not created.
>>>
>>> when I move the fan_data->alarm = alarm; out of fan_alarm_init() before
>>> devm_hwmon_device_register_with_groups() and the fan_alarm_init() after,
>>> then it works, and doesn't have a race condition.
>>>
>>> On master, populating fan_data->alarm_gpio is done in
>>> gpio_fan_get_of_data(fan_data); as far as I understand, so moving the
>>> fan_alarm_init() block further down shouldn't be a problem.
>>>
>>> I don't know, how I can test this with master kernel. Unfortunately, the
>>> device, I'm using doesn't have a recent kernel. And on my normal (desktop)
>>> pc, I don't have a gpio fan.
>>> How should I proceed now?
>>>
>>
>> Essentially, we'll need two patches: One to move fan_alarm_init() after
>> devm_hwmon_device_register_with_groups(), and then the notification patch.
>> For the backport to v4.9, the first patch will have to be slightly modified:
>> The first part will a simple
>>     fan_data->alarm = pdata->alarm;
>> at the location where fan_alarm_init() is called now, the second part is to move
>> the call to fan_alarm_init() after devm_hwmon_device_register_with_groups().
>>
>> It is ok to test the result with your 4.9 based kernel; we'll just have to be
>> careful when reviewing the mainline patch.
>>
>> Thanks,
>> Guenter
> 
> Ok,
> it seems like it is working as expected now on my 4.9 kernel. No race-condition and notification is received.
> I will adopt the changes to mainline kernel, but not sure if I can make it today. Might be Monday, till I have the patch.
> 
No hurry.

Thanks,
Guenter