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

[Guenter Roeck <linux@roeck-us.net>]

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. 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.

Guenter

> ---
> From: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> 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@linaro.org>
> Reported-by: kernel test robot <rong.a.chen@intel.com>
> Fixes: 7589238a8cf3 ("Revert "software node: Simplify software_node_release() function"")
> Suggested-by: "Rafael J. Wysocki" <rafael@kernel.org>
> Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> [ rjw: Drop parent reference only when called __kobject_del() ]
> Signed-off-by: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> ---
>  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
> 
> 
>