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

[arvindY]

On Friday 13 April 2018 07:59 AM, Chanwoo Choi wrote:
> On 2018ë 04ì 13ì 11:15, arvindY wrote:
> > 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.
> 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