Re: [PATCH] kobject: Avoid premature parent object freeing in kobject_cleanup()

[Andy Shevchenko]

On Mon, Aug 3, 2020 at 9:47 AM Qu Wenruo <quwenruo.btrfs@xxxxxxx> wrote:
> On 2020/6/5 äå1:46, Rafael J. Wysocki wrote:

...

> > +/**
> > + * kobject_del() - Unlink kobject from hierarchy.
> > + * @kobj: object.
> > + *
> > + * This is the function that should be called to delete an object
> > + * successfully added via kobject_add().
> > + */
> > +void kobject_del(struct kobject *kobj)
> > +{
> > +     struct kobject *parent = kobj->parent;
> > +
> > +     __kobject_del(kobj);
> > +     kobject_put(parent);
>
> Could you please add an extra check on kobj before accessing kobj->parent?

I do not understand. Where do we access it?
kobject_put() is NULL-aware.

> This patch in fact removes the ability to call kobject_del() on NULL
> pointer while not cause anything wrong.
>
> I know this is not a big deal, but such behavior change has already
> caused some problem for the incoming btrfs code.
> (Now I feels guilty just by looking into the old
> kobject_del()/kobject_put() and utilize that feature in btrfs)
>
> Since the old kobject_del() accepts NULL pointer intentionally, it would
> be much better to keep such behavior.

Can you elaborate, please?

-- 
With Best Regards,
Andy Shevchenko