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

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