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Message-ID: <CAHp75Ve0AozEbB_kc+S4qaZJxJJWf20toDK-T2QHYi1o2hfJBg@mail.gmail.com>
Date: Mon, 3 Aug 2020 10:27:50 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Qu Wenruo <quwenruo.btrfs@....com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Naresh Kamboju <naresh.kamboju@...aro.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
LKML <linux-kernel@...r.kernel.org>,
Linux ACPI <linux-acpi@...r.kernel.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Guenter Roeck <guenter@...ck-us.net>,
"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH] kobject: Avoid premature parent object freeing in kobject_cleanup()
On Mon, Aug 3, 2020 at 10:25 AM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Mon, Aug 3, 2020 at 9:47 AM Qu Wenruo <quwenruo.btrfs@....com> wrote:
> > On 2020/6/5 上午1:46, Rafael J. Wysocki wrote:
> > > +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.
Ah, I see, now.
Should be something like
struct kobject *parent = kobj ? kobj->parent : NULL;
> > 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.
--
With Best Regards,
Andy Shevchenko
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