linux-kernel - Re: [PATCHv5 01/10] Thermal: Do kfree in

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Date:	Mon, 03 Mar 2014 21:44:16 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Durgadoss R <durgadoss.r@...el.com>, eduardo.valentin@...com,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	hongbo.zhang@...escale.com, wni@...dia.com
Subject: Re: [PATCHv5 01/10] Thermal: Do kfree in _unregister functions

On Tue, 2014-01-21 at 11:46 -0800, Dmitry Torokhov wrote:
> Hi Durgadoss,
> 
> On Fri, Jan 17, 2014 at 05:26:18AM +0530, Durgadoss R wrote:
> > Currently the thermal_release function does
> > kfree for all devices when they call device_unregister.
> > This makes code scattering i.e whenever we add new
> > devices (to thermal class) we need to add its
> > corresponding kfree in thermal_release function.
> > And the if-else is also growing lengthy.
> > 
> > Instead, do all kfree() of devices in their own
> > _unregister functions. This makes the code look
> > clean and easy to maintain.
> > 
> > Signed-off-by: Durgadoss R <durgadoss.r@...el.com>
> > ---
> >  drivers/thermal/thermal_core.c |   17 +++++------------
> >  1 file changed, 5 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> > index 338a88b..165afc6 100644
> > --- a/drivers/thermal/thermal_core.c
> > +++ b/drivers/thermal/thermal_core.c
> > @@ -1042,18 +1042,7 @@ EXPORT_SYMBOL_GPL(thermal_zone_unbind_cooling_device);
> >  
> >  static void thermal_release(struct device *dev)
> >  {
> > -	struct thermal_zone_device *tz;
> > -	struct thermal_cooling_device *cdev;
> > -
> > -	if (!strncmp(dev_name(dev), "thermal_zone",
> > -		     sizeof("thermal_zone") - 1)) {
> > -		tz = to_thermal_zone(dev);
> > -		kfree(tz);
> > -	} else if(!strncmp(dev_name(dev), "cooling_device",
> > -			sizeof("cooling_device") - 1)){
> > -		cdev = to_cooling_device(dev);
> > -		kfree(cdev);
> > -	}
> > +	/* No-op since kfree(dev) is done in _unregister functions */
> >  }
> >  
> >  static struct class thermal_class = {
> > @@ -1146,6 +1135,7 @@ __thermal_cooling_device_register(struct device_node *np,
> >  unregister:
> >  	release_idr(&thermal_cdev_idr, &thermal_idr_lock, cdev->id);
> >  	device_unregister(&cdev->device);
> > +	kfree(cdev);
> 
> This is broken, you can not assume that you are holding the last
> reference. Please observe help text of DEBUG_KOBJECT_RELEASE config
> option, activate said option and try unregistering thermal device.
> 
agreed.
If you think it is too complicated to support the different thermal
components in thermal_release(), we can introduce per device .release()
callback as well.

thanks,
rui
> Thanks.
> 


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