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 2018ë 04ì 13ì 10:03, Chanwoo Choi wrote:
> > Hi,
> >
> > I'm sorry for the late reply.
> >
> > On 2018ë 03ì 30ì 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@xxxxxxxxx>
> > > ---
> > >   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