On 2020/6/5 上午1:46, Rafael J. Wysocki wrote: > From: Heikki Krogerus <[email protected]> > > 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 <[email protected]> > Reported-by: kernel test robot <[email protected]> > Fixes: 7589238a8cf3 ("Revert "software node: Simplify software_node_release() > function"") > Suggested-by: Rafael J. Wysocki <[email protected]> > Signed-off-by: Heikki Krogerus <[email protected]> > Signed-off-by: Rafael J. Wysocki <[email protected]> > --- > > 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?
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.
Or at least mention we require a valid kobject pointer.
Thanks,
Qu
> +}
> 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 +692,10 @@ static void kobject_cleanup(struct kobje
> 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);
> + } else {
> + /* avoid dropping the parent reference unnecessarily */
> + parent = NULL;
> }
>
> if (t && t->release) {
> @@ -698,6 +709,8 @@ static void kobject_cleanup(struct kobje
> pr_debug("kobject: '%s': free name\n", name);
> kfree_const(name);
> }
> +
> + kobject_put(parent);
> }
>
> #ifdef CONFIG_DEBUG_KOBJECT_RELEASE
>
>
>
>
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