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

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Date:   Thu, 11 Aug 2022 11:52:12 +0800
From:   haoxin <xhao@...ux.alibaba.com>
To:     Hyeonggon Yoo <42.hyeyoo@...il.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, xhao@...ux.alibaba.com
Subject: Re: [PATCH] mm/slub: release kobject if kobject_init_and_add failed
 in sysfs_slab_add


在 2022/8/11 上午11:31, Hyeonggon Yoo 写道:
> 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?

Yes,  I'm afraid think so， you can see the comment about kobject_add()

* Return: If this function returns an error, kobject_put() must be
  *         called to properly clean up the memory associated with the
  *         object.  Under no instance should the kobject that is passed
  *         to this function be directly freed with a call to kfree(),
  *         that can leak memory.
  *
  *         If this function returns success, kobject_put() must also be 
called
  *         in order to properly clean up the memory associated with the 
object.
  *
  *         In short, once this function is called, kobject_put() MUST 
be called
  *         when the use of the object is finished in order to properly free
  *         everything.
  */
int kobject_add(struct kobject *kobj, struct kobject *parent,
                 const char *fmt, ...)

>
> 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);
Maybe there use kobject_put will be better.
>> -	goto out;
>> +	return err;
>>   }
>>   
>>   void sysfs_slab_unlink(struct kmem_cache *s)
>> -- 
>> 2.31.0