linux-kernel - Re: [PATCH] kobject: Make sure the parent does not get released before its children

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Date:   Wed, 13 May 2020 17:42:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        kernel test robot <rong.a.chen@...el.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH] kobject: Make sure the parent does not get released
 before its children

On Wed, May 13, 2020 at 06:18:40PM +0300, Heikki Krogerus wrote:
> 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@...aro.org>
> Reported-by: kernel test robot <rong.a.chen@...el.com>
> Fixes: 7589238a8cf3 ("Revert "software node: Simplify software_node_release() function"")
> Cc: Brendan Higgins <brendanhiggins@...gle.com>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Suggested-by: "Rafael J. Wysocki" <rafael@...nel.org>
> Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> ---
>  lib/kobject.c | 30 ++++++++++++++++++++----------
>  1 file changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/kobject.c b/lib/kobject.c
> index 65fa7bf70c57..32432036bef8 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
> -- 
> 2.26.2
> 

Is this the older patch we talked about before, or something else?

I can't remember how we left that thread...

thanks,

greg k-h