Re: [PATCH v6] mm: cma: support sysfs

[Dmitry Osipenko]

24.03.2021 08:44, Minchan Kim пишет:
> On Tue, Mar 23, 2021 at 09:47:27PM -0700, John Hubbard wrote:
>> On 3/23/21 8:27 PM, Minchan Kim wrote:
>> ...
>>>>> +static int __init cma_sysfs_init(void)
>>>>> +{
>>>>> + unsigned int i;
>>>>> +
>>>>> + cma_kobj_root = kobject_create_and_add("cma", mm_kobj);
>>>>> + if (!cma_kobj_root)
>>>>> +         return -ENOMEM;
>>>>> +
>>>>> + for (i = 0; i < cma_area_count; i++) {
>>>>> +         int err;
>>>>> +         struct cma *cma;
>>>>> +         struct cma_kobject *cma_kobj;
>>>>> +
>>>>> +         cma_kobj = kzalloc(sizeof(*cma_kobj), GFP_KERNEL);
>>>>> +         if (!cma_kobj) {
>>>>> +                 kobject_put(cma_kobj_root);
>>>>> +                 return -ENOMEM;
>>>>
>>>> This leaks little cma_kobj's all over the floor. :)
>>>
>>> I thought kobject_put(cma_kobj_root) should deal with it. No?
>>>
>> If this fails when i > 0, there will be cma_kobj instances that
>> were stashed in the cma_areas[] array. But this code only deletes
>> the most recently allocated cma_kobj, not anything allocated on
>> previous iterations of the loop.
> 
> Oh, I misunderstood that destroying of root kobject will release
> children recursively. Seems not true. Go back to old version.
> 
> 
> index 16c81c9cb9b7..418951a3f138 100644
> --- a/mm/cma_sysfs.c
> +++ b/mm/cma_sysfs.c
> @@ -80,20 +80,19 @@ static struct kobj_type cma_ktype = {
>  static int __init cma_sysfs_init(void)
>  {
>         unsigned int i;
> +       int err;
> +       struct cma *cma;
> +       struct cma_kobject *cma_kobj;
> 
>         cma_kobj_root = kobject_create_and_add("cma", mm_kobj);
>         if (!cma_kobj_root)
>                 return -ENOMEM;
> 
>         for (i = 0; i < cma_area_count; i++) {
> -               int err;
> -               struct cma *cma;
> -               struct cma_kobject *cma_kobj;
> -
>                 cma_kobj = kzalloc(sizeof(*cma_kobj), GFP_KERNEL);
>                 if (!cma_kobj) {
> -                       kobject_put(cma_kobj_root);
> -                       return -ENOMEM;
> +                       err = -ENOMEM;
> +                       goto out;
>                 }
> 
>                 cma = &cma_areas[i];
> @@ -103,11 +102,21 @@ static int __init cma_sysfs_init(void)
>                                            cma_kobj_root, "%s", cma->name);
>                 if (err) {
>                         kobject_put(&cma_kobj->kobj);
> -                       kobject_put(cma_kobj_root);
> -                       return err;
> +                       goto out;
>                 }
>         }
> 
>         return 0;
> +out:
> +       while (--i >= 0) {
> +               cma = &cma_areas[i];
> +
> +               kobject_put(&cma->kobj->kobj);
> +               kfree(cma->kobj);
> +               cma->kobj = NULL;
> +       }
> +       kobject_put(cma_kobj_root);
> +
> +       return err;
>  }
>  subsys_initcall(cma_sysfs_init);

Since we don't care about the order in which kobjects are put, I'd write it in 
this way, which I think looks cleaner:

static void cma_sysfs_cleanup(struct kobject *cma_kobj_root)
{
        struct cma *cma = cma_areas;
        unsigned int i;

        for (i = 0; i < cma_area_count; i++, cma++) {
                if (!cma->kobj)
                        break;

                kobject_put(&cma->kobj->kobj);
        }

        kobject_put(cma_kobj_root);
}

static int __init cma_sysfs_init(void)
{
        struct kobject *cma_kobj_root;
        unsigned int i;

        cma_kobj_root = kobject_create_and_add("cma", mm_kobj);
        if (!cma_kobj_root)
                return -ENOMEM;

        for (i = 0; i < cma_area_count; i++) {
                struct cma_kobject *cma_kobj;
                struct cma *cma;
                int err;

                cma_kobj = kzalloc(sizeof(*cma_kobj), GFP_KERNEL);
                if (!cma_kobj) {
                        cma_sysfs_cleanup(cma_kobj_root);
                        return -ENOMEM;
                }

                cma = &cma_areas[i];
                cma->kobj = cma_kobj;
                cma_kobj->cma = cma;
                err = kobject_init_and_add(&cma_kobj->kobj, &cma_ktype,
                                           cma_kobj_root, "%s", cma->name);
                if (err) {
                        cma_sysfs_cleanup(cma_kobj_root);
                        return err;
                }
        }

        return 0;
}
subsys_initcall(cma_sysfs_init);