Re: [PATCH] mm/slub: release kobject if kobject_init_and_add failed in sysfs_slab_add

[haoxin]

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@xxxxxxxxxxxxxxxxx>
> > ---
> >   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