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

[Guenter Roeck]

On 5/28/20 3:57 AM, Rafael J. Wysocki wrote:
> 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.
> 

The failing arm boot tests are due to various dts changes (commit "arm64:
dts: vexpress: Move fixed devices out of bus node" and associated),
unrelated to this patch.

Guenter

> 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
>>>
>>>
>>>