On Mon, Aug 03, 2020 at 02:31:23PM +0800, Qu Wenruo wrote:
>
>
> On 2020/6/5 上午1:46, Rafael J. Wysocki wrote:
> > From: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> >
> > If kobject_del() is invoked by kobject_cleanup() to delete the
> > target kobject, it may cause its parent kobject to be freed
> > before invoking the target kobject's ->release() method, which
> > effectively means freeing the parent before dealing with the
> > child entirely.
> >
> > That is confusing at best and it may also lead to functional
> > issues if the callers of kobject_cleanup() are not careful enough
> > about the order in which these calls are made, so avoid the
> > problem by making kobject_cleanup() drop the last reference to
> > the target kobject's parent at the end, after invoking the target
> > kobject's ->release() method.
> >
> > [ rjw: Rewrite the subject and changelog, make kobject_cleanup()
> > drop the parent reference only when __kobject_del() 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>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > ---
> >
> > Hi Greg,
> >
> > This is a replacement for commit 4ef12f719802 ("kobject: Make sure the parent
> > does not get released before its children"), that you reverted, because it
> > broke things and the reason why was that it was incorrect.
> >
> > Namely, it called kobject_put() on the target kobject's parent in
> > kobject_cleanup() unconditionally, but it should only call it after
> > invoking __kobject_del() on the target kobject.
> >
> > That problem is fixed in this patch and a functionally equivalent patch has
> > been tested by Guenter without issues.
> >
> > The underlying issue addressed by the reverted commit is still there and
> > it may show up again even though the test that triggered it originally was
> > fixed in the meantime. IMO it is worth fixing even though it may not be
> > readily visible in the current kernel, so please consider this one for
> > applying.
> >
> > Cheers!
> >
> > ---
> > lib/kobject.c | 33 +++++++++++++++++++++++----------
> > 1 file changed, 23 insertions(+), 10 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);
>
> Could you please add an extra check on kobj before accessing kobj->parent?
Sure, please just send a patch for this.
thanks,
greg k-h
