Re: [PATCH 2/2] kobject: send KOBJ_REMOVE uevent when the object is removed from sysfs

[Rafael J. Wysocki]

On Thu, May 28, 2020 at 12:25 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> On Wed, May 27, 2020 at 11:01:16AM +0200, Rafael J. Wysocki wrote:
> >
> > So Guenter, can you please test the patch below to see if it still introduces
> > the problems seen by you on ARM?
> >
>
> arm64 and arm64be boot tests pass with the patch below.

Great, thanks!

> Some arm boot tests fail, but I think that is due to some other problem with -next.
> Hard to say for sure at this point because -next is pretty badly broken
> overall. I'll need to run some bisects to see what is going on.

I see.

Thanks for giving this one a go.

> > ---
> > From: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> > Subject: [PATCH] kobject: Make sure the parent does not get released before its children
> >
> > In the function kobject_cleanup(), kobject_del(kobj) is
> > called before the kobj->release(). That makes it possible to
> > release the parent of the kobject before the kobject itself.
> >
> > To fix that, adding function __kboject_del() that does
> > everything that kobject_del() does except release the parent
> > reference. kobject_cleanup() then calls __kobject_del()
> > instead of kobject_del(), and separately decrements the
> > reference count of the parent kobject after kobj->release()
> > has been called.
> >
> > Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
> > Reported-by: kernel test robot <rong.a.chen@xxxxxxxxx>
> > Fixes: 7589238a8cf3 ("Revert "software node: Simplify software_node_release() function"")
> > Suggested-by: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> > Signed-off-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> > [ rjw: Drop parent reference only when called __kobject_del() ]
> > Signed-off-by: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
> > ---
> >  lib/kobject.c |   34 +++++++++++++++++++++++-----------
> >  1 file changed, 23 insertions(+), 11 deletions(-)
> >
> > Index: linux-pm/lib/kobject.c
> > ===================================================================
> > --- linux-pm.orig/lib/kobject.c
> > +++ linux-pm/lib/kobject.c
> > @@ -599,14 +599,7 @@ out:
> >  }
> >  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);
> >
> >  /**
> > @@ -663,7 +670,9 @@ 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);
> > +     bool state_in_sysfs = kobj->state_in_sysfs;
> >       const char *name = kobj->name;
> >
> >       pr_debug("kobject: '%s' (%p): %s, parent %p\n",
> > @@ -681,10 +690,10 @@ static void kobject_cleanup(struct kobje
> >       }
> >
> >       /* remove from sysfs if the caller did not do it */
> > -     if (kobj->state_in_sysfs) {
> > +     if (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 +707,9 @@ static void kobject_cleanup(struct kobje
> >               pr_debug("kobject: '%s': free name\n", name);
> >               kfree_const(name);
> >       }
> > +
> > +     if (state_in_sysfs)
> > +             kobject_put(parent);
> >  }
> >
> >  #ifdef CONFIG_DEBUG_KOBJECT_RELEASE
> >
> >
> >