linux-kernel - Re: [PATCH] mm/slub: release kobject if kobject_init_and_add failed in sysfs_slab

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Message-ID: <YvR4GqAqykjUwBJn@ip-172-31-24-42.ap-northeast-1.compute.internal>
Date:   Thu, 11 Aug 2022 03:31:38 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Xin Hao <xhao@...ux.alibaba.com>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org, vbabka@...e.cz,
        roman.gushchin@...ux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slub: release kobject if kobject_init_and_add failed
 in sysfs_slab_add

On Thu, Aug 11, 2022 at 10:52:58AM +0800, Xin Hao wrote:
> In kobject_init_and_add() function, the refcount is setted by calling
> kobject_init() function, regardless of whether the return value is zero
> or not, therefore, we must call kobject_del(&s->kobj) to prevent memory

Hello and thanks!

Should kobject_del() be called when kobject_add() failed?

its comments says:

 597  * kobject_del() - Unlink kobject from hierarchy.
 598  * @kobj: object.
 599  *
 600  * This is the function that should be called to delete an object
 601  * successfully added via kobject_add().

AFAIK kobject_put() is proper function to call when
kobject_init_and_add() failed as stated in its comment:

 417 /**
 418  * kobject_init_and_add() - Initialize a kobject structure and add it to
 419  *                          the kobject hierarchy.
 420  * @kobj: pointer to the kobject to initialize
 421  * @ktype: pointer to the ktype for this kobject.
 422  * @parent: pointer to the parent of this kobject.
 423  * @fmt: the name of the kobject.
 424  *
 425  * This function combines the call to kobject_init() and kobject_add().
 426  *
 427  * If this function returns an error, kobject_put() must be called to
 428  * properly clean up the memory associated with the object.  This is the
 429  * same type of error handling after a call to kobject_add() and kobject
 430  * lifetime rules are the same here.

> of s->kobj is leaked.
> 
> Signed-off-by: Xin Hao <xhao@...ux.alibaba.com>
> ---
>  mm/slub.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index b1281b8654bd..63b0a8a3a71f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5981,19 +5981,18 @@ static int sysfs_slab_add(struct kmem_cache *s)
>  
>  	err = sysfs_create_group(&s->kobj, &slab_attr_group);
>  	if (err)
> -		goto out_del_kobj;
> +		goto out;
>  
>  	if (!unmergeable) {
>  		/* Setup first alias */
>  		sysfs_slab_alias(s, s->name);
>  	}
> +	return err;
>  out:
>  	if (!unmergeable)
>  		kfree(name);
> -	return err;
> -out_del_kobj:
>  	kobject_del(&s->kobj);
> -	goto out;
> +	return err;
>  }
>  
>  void sysfs_slab_unlink(struct kmem_cache *s)
> -- 
> 2.31.0