linux-kernel - Re: [PATCH v1] kobject: make sure parent is not released before children

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Date:   Mon, 20 Apr 2020 15:03:41 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        lkft-triage@...ts.linaro.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v1] kobject: make sure parent is not released before children

On Fri, Apr 17, 2020 at 9:08 AM Randy Dunlap <rdunlap@...radead.org> wrote:
>
> On 4/17/20 4:39 AM, Heikki Krogerus wrote:
> > Hi,
> >
> >>>> An alternative might be to define something like __kobject_del() doing
> >>>> everything that kobject_del() does *without* the
> >>>> kobject_put(kobj->parent).
> >>>>
> >>>> Then, kobject_del() could be defined as something like (pseudocode):
> >>>>
> >>>> kobject_del(kobj)
> >>>> {
> >>>>     kobject *perent = kobj->parent;
> >>>>
> >>>>     __kobject_del(kobj);
> >>>>     kobject_put(parent);
> >>>> }
> >>>>
> >>>> and kobject_cleanup() could call __kobject_del() instead of
> >>>> kobject_del() and then do the last kobject_put(parent) when it is done
> >>>> with the child.
> >>>>
> >>>> Would that work?
> >>>
> >>> I think so. Greg, what do you think?
> >>
> >> Hm, maybe.  Can someone test it out with the reproducer?
> >
> > Brendan, or Randy! Can you guys test Rafael's proposal? I think it
> > would look like this:
>
> patch is whitespace-damaged. did you copy-paste it from a screen?
>
>
> Anyway, it works for me. I loaded & unloaded test_printf.ko 5 times
> without a problem.

I just tried it as well. I also noticed some whitespace corruption,
but it otherwise worked against the KUnit reproducer I wrote:

https://lore.kernel.org/patchwork/patch/1224002/

Thanks!

> Thanks.
>
> > diff --git a/lib/kobject.c b/lib/kobject.c
> > index 83198cb37d8d..2bd631460e18 100644
> > --- a/lib/kobject.c
> > +++ b/lib/kobject.c
> > @@ -599,14 +599,7 @@ int kobject_move(struct kobject *kobj, struct kobject *new_parent)
> >  }
> >  EXPORT_SYMBOL_GPL(kobject_move);
> >
> > -/**
> > - * 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)
> > +static void __kobject_del(struct kobject *kobj)
> >  {
> >         struct kernfs_node *sd;
> >         const struct kobj_type *ktype;
> > @@ -625,9 +618,23 @@ void kobject_del(struct kobject *kobj)
> >
> >         kobj->state_in_sysfs = 0;
> >         kobj_kset_leave(kobj);
> > -       kobject_put(kobj->parent);
> >         kobj->parent = NULL;
> >  }
> > +
> > +/**
> > + * 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);
> > +}
> >  EXPORT_SYMBOL(kobject_del);
> >
> >  /**
> > @@ -663,6 +670,7 @@ EXPORT_SYMBOL(kobject_get_unless_zero);
> >   */
> >  static void kobject_cleanup(struct kobject *kobj)
> >  {
> > +       struct kobject *parent = kobj->parent;
> >         struct kobj_type *t = get_ktype(kobj);
> >         const char *name = kobj->name;
> >
> > @@ -684,7 +692,7 @@ static void kobject_cleanup(struct kobject *kobj)
> >         if (kobj->state_in_sysfs) {
> >                 pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n",
> >                          kobject_name(kobj), kobj);
> > -               kobject_del(kobj);
> > +               __kobject_del(kobj);
> >         }
> >
> >         if (t && t->release) {
> > @@ -698,6 +706,8 @@ static void kobject_cleanup(struct kobject *kobj)
> >                 pr_debug("kobject: '%s': free name\n", name);
> >                 kfree_const(name);
> >         }
> > +
> > +       kobject_put(parent);
> >  }
> >
> >  #ifdef CONFIG_DEBUG_KOBJECT_RELEASE
> >
> >
> > thanks,
> >
>
>
> --
> ~Randy
> Reported-by: Randy Dunlap <rdunlap@...radead.org>