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SubjectRe: [PATCH V2 1/1] mm/slub: release kobject if kobject_init_and_add failed in sysfs_slab_add
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在 2022/8/14 下午4:05, Hyeonggon Yoo 写道:
> On Thu, Aug 11, 2022 at 03:18:44PM +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
>> of s->kobj is leaked.
> TL;DR: IIUC current code works just fine
>
> After thinking more, I don't think the memory leak you said exist.
> The space for s->kobj is freed in create_cache() when __kmem_cache_create() failed.

Yes, Agree what you explain,  but  in slab_sysfs_init() function, it
also call slab_sysfs_add() and  there no other function to release it, 
so i think the memory leak still exist.

> The situation here is:
>
> create_cache() {
> s = kmem_cache_alloc(kmem_cache, GFP_KERNEL)
> err = __kmem_cache_create()
> if (err)
> goto out_free_cache;
>
> out_free_cache:
> kmem_cache_free(s) // s is freed here (including its kobject)
> [...]
> }
>
> __kmem_cache_create() {
> [...]
>
> err = sysfs_slab_add();
> if (err) {
> __kmem_cache_release(s);
> return err;
> }
> }
>
> The primary goal of kobject_put() is to call release() function
> of kobj_type (when reference becomes zero), which is kmem_cache_release().
>
> kmem_cache_release() {
> __kmem_cache_release(s)
> kfree_const(s->name)
> kmem_cache_free(s)
> }
>
> But when slab_sysfs_add() failed, __kmem_cache_release() and
> create_cache() releases resources related to the cache.
> (Also its name is freed in kmem_cache_create_usercopy().)
>
> So IIUC current code works just fine!
>
>> Signed-off-by: Xin Hao <xhao@linux.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..940a3f52e07c 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);
>> + kobject_put(&s->kobj);
>> return err;
>> -out_del_kobj:
>> - kobject_del(&s->kobj);
> So related resources are released in create_cache(), instead of by
> calling kobject_put().
>
> But kobject_del() is still needed because it should unlink kobject
> hierarchy when kobject_add() succeeded but sysfs_create_group() failed!
>
>> - goto out;
>> }
>>
>> void sysfs_slab_unlink(struct kmem_cache *s)
>> --
>> 2.31.0
>>

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