[PATCH] PM / devfreq: use put_device() instead of kfree()

[PATCH] PM / devfreq: use put_device() instead of kfree()

[Arvind Yadav]

Never directly free @dev after calling device_register() or
device_unregister(), even if device_register() returned an error.
Always use put_device() to give up the reference initialized.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
---
 drivers/devfreq/devfreq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index fe2af6a..a225b94 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	err = device_register(&devfreq->dev);
 	if (err) {
 		mutex_unlock(&devfreq->lock);
-		goto err_dev;
+		put_device(&devfreq->dev);
+		goto err_out;
 	}
 
 	devfreq->trans_table =	devm_kzalloc(&devfreq->dev,
@@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	mutex_unlock(&devfreq_list_lock);
 
 	device_unregister(&devfreq->dev);
+	devfreq = NULL;
 err_dev:
 	if (devfreq)
 		kfree(devfreq);
-- 
2.7.4

Re: [PATCH] PM / devfreq: use put_device() instead of kfree()

[Chanwoo Choi]

Hi,

I'm sorry for the late reply.

On 2018년 03월 30일 20:44, Arvind Yadav wrote:
> Never directly free @dev after calling device_register() or
> device_unregister(), even if device_register() returned an error.
> Always use put_device() to give up the reference initialized.
> 
> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
> ---
>  drivers/devfreq/devfreq.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index fe2af6a..a225b94 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  	err = device_register(&devfreq->dev);
>  	if (err) {
>  		mutex_unlock(&devfreq->lock);
> -		goto err_dev;
> +		put_device(&devfreq->dev);
> +		goto err_out;

why do you change the goto postion?
err_out is correct to free the memory of devfreq instance.

>  	}
>  
>  	devfreq->trans_table =	devm_kzalloc(&devfreq->dev,
> @@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  	mutex_unlock(&devfreq_list_lock);
>  
>  	device_unregister(&devfreq->dev);
> +	devfreq = NULL;

It is wrong. If you initialize the devfreq as NULL,
never free the 'devfreq' instance.

>  err_dev:
>  	if (devfreq)
>  		kfree(devfreq);
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [PATCH] PM / devfreq: use put_device() instead of kfree()

[Chanwoo Choi]

On 2018년 04월 13일 10:03, Chanwoo Choi wrote:
> Hi,
> 
> I'm sorry for the late reply.
> 
> On 2018년 03월 30일 20:44, Arvind Yadav wrote:
>> Never directly free @dev after calling device_register() or
>> device_unregister(), even if device_register() returned an error.
>> Always use put_device() to give up the reference initialized.
>>
>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
>> ---
>>  drivers/devfreq/devfreq.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index fe2af6a..a225b94 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>  	err = device_register(&devfreq->dev);
>>  	if (err) {
>>  		mutex_unlock(&devfreq->lock);
>> -		goto err_dev;
>> +		put_device(&devfreq->dev);
>> +		goto err_out;
> 
> why do you change the goto postion?
> err_out is correct to free the memory of devfreq instance.

Sorry. err_dev is correct instead of err_out.

> 
>>  	}
>>  
>>  	devfreq->trans_table =	devm_kzalloc(&devfreq->dev,
>> @@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>  	mutex_unlock(&devfreq_list_lock);
>>  
>>  	device_unregister(&devfreq->dev);
>> +	devfreq = NULL;
> 
> It is wrong. If you initialize the devfreq as NULL,
> never free the 'devfreq' instance.
> 
>>  err_dev:
>>  	if (devfreq)
>>  		kfree(devfreq);
>>
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [PATCH] PM / devfreq: use put_device() instead of kfree()

[arvindY]

Hi Chanwoo,

On Friday 13 April 2018 06:43 AM, Chanwoo Choi wrote:
> On 2018년 04월 13일 10:03, Chanwoo Choi wrote:
>> Hi,
>>
>> I'm sorry for the late reply.
>>
>> On 2018년 03월 30일 20:44, Arvind Yadav wrote:
>>> Never directly free @dev after calling device_register() or
>>> device_unregister(), even if device_register() returned an error.
>>> Always use put_device() to give up the reference initialized.
>>>
>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
>>> ---
>>>   drivers/devfreq/devfreq.c | 4 +++-
>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index fe2af6a..a225b94 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>   	err = device_register(&devfreq->dev);
>>>   	if (err) {
>>>   		mutex_unlock(&devfreq->lock);
>>> -		goto err_dev;
>>> +		put_device(&devfreq->dev);
>>> +		goto err_out;
>> why do you change the goto postion?
>> err_out is correct to free the memory of devfreq instance.
> Sorry. err_dev is correct instead of err_out.

If you will see the comment for device_register(drivers/base/core.c)
there is mentioned that 'NOTE: _Never_ directly free @dev
after calling this function, even if it returned an error!
Always use put_device() to give up the reference initialized
in this function instead. Here  put_device() will decrement
the last reference and then free the memory by calling dev->release.
Internally put_device() -> kobject_put() -> kobject_cleanup() which
is responsible to call 'dev -> release' and also free other kobject 
resources.

We are releasing devfreq in devfreq_dev_release(). So no need
to call kfree() again. It'll be redundant.  'err_out' is correct.
>
>>>   	}
>>>   
>>>   	devfreq->trans_table =	devm_kzalloc(&devfreq->dev,
>>> @@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>   	mutex_unlock(&devfreq_list_lock);
>>>   
>>>   	device_unregister(&devfreq->dev);
>>> +	devfreq = NULL;
>> It is wrong. If you initialize the devfreq as NULL,
>> never free the 'devfreq' instance.

No need to release memory after device_unregister().
driver core will take care of this. It will release memory
So no need to call free again.
>>
>>>   err_dev:
>>>   	if (devfreq)
>>>   		kfree(devfreq);
>>>
>>
>

~arvind

Re: [PATCH] PM / devfreq: use put_device() instead of kfree()

[Chanwoo Choi]

On 2018년 04월 13일 11:15, arvindY wrote:
> Hi Chanwoo,
> 
> On Friday 13 April 2018 06:43 AM, Chanwoo Choi wrote:
>> On 2018년 04월 13일 10:03, Chanwoo Choi wrote:
>>> Hi,
>>>
>>> I'm sorry for the late reply.
>>>
>>> On 2018년 03월 30일 20:44, Arvind Yadav wrote:
>>>> Never directly free @dev after calling device_register() or
>>>> device_unregister(), even if device_register() returned an error.
>>>> Always use put_device() to give up the reference initialized.
>>>>
>>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
>>>> ---
>>>>   drivers/devfreq/devfreq.c | 4 +++-
>>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>> index fe2af6a..a225b94 100644
>>>> --- a/drivers/devfreq/devfreq.c
>>>> +++ b/drivers/devfreq/devfreq.c
>>>> @@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>       err = device_register(&devfreq->dev);
>>>>       if (err) {
>>>>           mutex_unlock(&devfreq->lock);
>>>> -        goto err_dev;
>>>> +        put_device(&devfreq->dev);
>>>> +        goto err_out;
>>> why do you change the goto postion?
>>> err_out is correct to free the memory of devfreq instance.
>> Sorry. err_dev is correct instead of err_out.
> 
> If you will see the comment for device_register(drivers/base/core.c)
> there is mentioned that 'NOTE: _Never_ directly free @dev
> after calling this function, even if it returned an error!
> Always use put_device() to give up the reference initialized
> in this function instead. Here  put_device() will decrement
> the last reference and then free the memory by calling dev->release.
> Internally put_device() -> kobject_put() -> kobject_cleanup() which
> is responsible to call 'dev -> release' and also free other kobject resources.
> 
> We are releasing devfreq in devfreq_dev_release(). So no need
> to call kfree() again. It'll be redundant.  'err_out' is correct.

You're right. err_out is correct.
put_device() -> dev->release() -> devfreq_dev_release() -> kfree(devfreq)

>>
>>>>       }
>>>>         devfreq->trans_table =    devm_kzalloc(&devfreq->dev,
>>>> @@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>       mutex_unlock(&devfreq_list_lock);
>>>>         device_unregister(&devfreq->dev);
>>>> +    devfreq = NULL;
>>> It is wrong. If you initialize the devfreq as NULL,
>>> never free the 'devfreq' instance.
> 
> No need to release memory after device_unregister().
> driver core will take care of this. It will release memory
> So no need to call free again.

If you have to initialize the devfreq instance as NULL,
I think that you better to init in the devfreq_dev_release()
as following:

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index fe2af6aa88fc..8c52a13d3887 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -543,6 +543,7 @@ static void devfreq_dev_release(struct device *dev)
 
        mutex_destroy(&devfreq->lock);
        kfree(devfreq);
+       devfreq = NULL;
 }


>>>
>>>>   err_dev:
>>>>       if (devfreq)
>>>>           kfree(devfreq);
>>>>
>>>
>>
> 
> ~arvind
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [PATCH] PM / devfreq: use put_device() instead of kfree()

[arvindY]

On Friday 13 April 2018 07:59 AM, Chanwoo Choi wrote:
> On 2018년 04월 13일 11:15, arvindY wrote:
>> Hi Chanwoo,
>>
>> On Friday 13 April 2018 06:43 AM, Chanwoo Choi wrote:
>>> On 2018년 04월 13일 10:03, Chanwoo Choi wrote:
>>>> Hi,
>>>>
>>>> I'm sorry for the late reply.
>>>>
>>>> On 2018년 03월 30일 20:44, Arvind Yadav wrote:
>>>>> Never directly free @dev after calling device_register() or
>>>>> device_unregister(), even if device_register() returned an error.
>>>>> Always use put_device() to give up the reference initialized.
>>>>>
>>>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
>>>>> ---
>>>>>    drivers/devfreq/devfreq.c | 4 +++-
>>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>>> index fe2af6a..a225b94 100644
>>>>> --- a/drivers/devfreq/devfreq.c
>>>>> +++ b/drivers/devfreq/devfreq.c
>>>>> @@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>>        err = device_register(&devfreq->dev);
>>>>>        if (err) {
>>>>>            mutex_unlock(&devfreq->lock);
>>>>> -        goto err_dev;
>>>>> +        put_device(&devfreq->dev);
>>>>> +        goto err_out;
>>>> why do you change the goto postion?
>>>> err_out is correct to free the memory of devfreq instance.
>>> Sorry. err_dev is correct instead of err_out.
>> If you will see the comment for device_register(drivers/base/core.c)
>> there is mentioned that 'NOTE: _Never_ directly free @dev
>> after calling this function, even if it returned an error!
>> Always use put_device() to give up the reference initialized
>> in this function instead. Here  put_device() will decrement
>> the last reference and then free the memory by calling dev->release.
>> Internally put_device() -> kobject_put() -> kobject_cleanup() which
>> is responsible to call 'dev -> release' and also free other kobject resources.
>>
>> We are releasing devfreq in devfreq_dev_release(). So no need
>> to call kfree() again. It'll be redundant.  'err_out' is correct.
> You're right. err_out is correct.
> put_device() -> dev->release() -> devfreq_dev_release() -> kfree(devfreq)
>
>>>>>        }
>>>>>          devfreq->trans_table =    devm_kzalloc(&devfreq->dev,
>>>>> @@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>>        mutex_unlock(&devfreq_list_lock);
>>>>>          device_unregister(&devfreq->dev);
>>>>> +    devfreq = NULL;
>>>> It is wrong. If you initialize the devfreq as NULL,
>>>> never free the 'devfreq' instance.
>> No need to release memory after device_unregister().
>> driver core will take care of this. It will release memory
>> So no need to call free again.
> If you have to initialize the devfreq instance as NULL,
> I think that you better to init in the devfreq_dev_release()
> as following:
>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index fe2af6aa88fc..8c52a13d3887 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -543,6 +543,7 @@ static void devfreq_dev_release(struct device *dev)
>   
>          mutex_destroy(&devfreq->lock);
>          kfree(devfreq);
> +       devfreq = NULL;
>   }

Yes, You are right. I will share a update patch.
Thanks for reviewing.
>
>>>>>    err_dev:
>>>>>        if (devfreq)
>>>>>            kfree(devfreq);
>>>>>
>> ~arvind
>>
>>
>>
>

Re: [PATCH] PM / devfreq: use put_device() instead of kfree()

[Chanwoo Choi]

On 2018년 04월 13일 11:37, arvindY wrote:
> 
> 
> On Friday 13 April 2018 07:59 AM, Chanwoo Choi wrote:
>> On 2018년 04월 13일 11:15, arvindY wrote:
>>> Hi Chanwoo,
>>>
>>> On Friday 13 April 2018 06:43 AM, Chanwoo Choi wrote:
>>>> On 2018년 04월 13일 10:03, Chanwoo Choi wrote:
>>>>> Hi,
>>>>>
>>>>> I'm sorry for the late reply.
>>>>>
>>>>> On 2018년 03월 30일 20:44, Arvind Yadav wrote:
>>>>>> Never directly free @dev after calling device_register() or
>>>>>> device_unregister(), even if device_register() returned an error.
>>>>>> Always use put_device() to give up the reference initialized.
>>>>>>
>>>>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
>>>>>> ---
>>>>>>    drivers/devfreq/devfreq.c | 4 +++-
>>>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>>>> index fe2af6a..a225b94 100644
>>>>>> --- a/drivers/devfreq/devfreq.c
>>>>>> +++ b/drivers/devfreq/devfreq.c
>>>>>> @@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>>>        err = device_register(&devfreq->dev);
>>>>>>        if (err) {
>>>>>>            mutex_unlock(&devfreq->lock);
>>>>>> -        goto err_dev;
>>>>>> +        put_device(&devfreq->dev);
>>>>>> +        goto err_out;
>>>>> why do you change the goto postion?
>>>>> err_out is correct to free the memory of devfreq instance.
>>>> Sorry. err_dev is correct instead of err_out.
>>> If you will see the comment for device_register(drivers/base/core.c)
>>> there is mentioned that 'NOTE: _Never_ directly free @dev
>>> after calling this function, even if it returned an error!
>>> Always use put_device() to give up the reference initialized
>>> in this function instead. Here  put_device() will decrement
>>> the last reference and then free the memory by calling dev->release.
>>> Internally put_device() -> kobject_put() -> kobject_cleanup() which
>>> is responsible to call 'dev -> release' and also free other kobject resources.
>>>
>>> We are releasing devfreq in devfreq_dev_release(). So no need
>>> to call kfree() again. It'll be redundant.  'err_out' is correct.
>> You're right. err_out is correct.
>> put_device() -> dev->release() -> devfreq_dev_release() -> kfree(devfreq)
>>
>>>>>>        }
>>>>>>          devfreq->trans_table =    devm_kzalloc(&devfreq->dev,
>>>>>> @@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>>>        mutex_unlock(&devfreq_list_lock);
>>>>>>          device_unregister(&devfreq->dev);
>>>>>> +    devfreq = NULL;
>>>>> It is wrong. If you initialize the devfreq as NULL,
>>>>> never free the 'devfreq' instance.
>>> No need to release memory after device_unregister().
>>> driver core will take care of this. It will release memory
>>> So no need to call free again.
>> If you have to initialize the devfreq instance as NULL,
>> I think that you better to init in the devfreq_dev_release()
>> as following:
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index fe2af6aa88fc..8c52a13d3887 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -543,6 +543,7 @@ static void devfreq_dev_release(struct device *dev)
>>            mutex_destroy(&devfreq->lock);
>>          kfree(devfreq);
>> +       devfreq = NULL;
>>   }
> 
> Yes, You are right. I will share a update patch.
> Thanks for reviewing.

It is my mistake. 'devfreq' is local variable in the devfreq_dev_release(0.  
Even if initializes 'devfreq = NULL' in the devfreq_dev_release(),
it cannot initialize the 'devfreq' local variable in the devfreq_add_device().

I think that your original patch is good.
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

>>
>>>>>>    err_dev:
>>>>>>        if (devfreq)
>>>>>>            kfree(devfreq);
>>>>>>
>>> ~arvind
>>>
>>>
>>>
>>
> 
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

RE: Re: [PATCH] PM / devfreq: use put_device() instead of kfree()

[MyungJoo Ham]

>On 2018년 04월 13일 11:37, arvindY wrote:
>> On Friday 13 April 2018 07:59 AM, Chanwoo Choi wrote:
>>> On 2018년 04월 13일 11:15, arvindY wrote:
>>>> On Friday 13 April 2018 06:43 AM, Chanwoo Choi wrote:
>>>>> On 2018년 04월 13일 10:03, Chanwoo Choi wrote:
[]
>>>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>>>>> index fe2af6a..a225b94 100644
>>>>>>> --- a/drivers/devfreq/devfreq.c
>>>>>>> +++ b/drivers/devfreq/devfreq.c
>>>>>>> @@ -625,7 +625,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>>>>        err = device_register(&devfreq->dev);
>>>>>>>        if (err) {
>>>>>>>            mutex_unlock(&devfreq->lock);
>>>>>>> -        goto err_dev;
>>>>>>> +        put_device(&devfreq->dev);
>>>>>>> +        goto err_out;
>>>>>>>        }
>>>>>>>          devfreq->trans_table =    devm_kzalloc(&devfreq->dev,
>>>>>>> @@ -671,6 +672,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>>>>>>        mutex_unlock(&devfreq_list_lock);
>>>>>>>          device_unregister(&devfreq->dev);
>>>>>>> +    devfreq = NULL;
>>>>>>>    err_dev:
>>>>>>>        if (devfreq)
>>>>>>>            kfree(devfreq);
>>>>>>>

Ah.. this was critcal. Thanks!

Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>

>Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>


Cheers,
MyungJoo