On 2021/4/1 11:35, Roman Gushchin wrote:
> On Thu, Apr 01, 2021 at 11:31:16AM +0800, Miaohe Lin wrote:
>> On 2021/4/1 11:01, Muchun Song wrote:
>>> Christian Borntraeger reported a warning about "percpu ref
>>> (obj_cgroup_release) <= 0 (-1) after switching to atomic".
>>> Because we forgot to obtain the reference to the objcg and
>>> wrongly obtain the reference of memcg.
>>>
>>> Reported-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
>>> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
>>
>> Thanks for the patch.
>> Is a Fixes tag needed?
>
> No, as the original patch hasn't been merged into the Linus's tree yet.
> So the fix can be simply squashed.
>
> Btw, the fix looks good to me.
>
> Acked-by: Roman Gushchin <guro@xxxxxx>
>
I see. Many thanks for explanation!
The code looks good to me.
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>>
>>> ---
>>> include/linux/memcontrol.h | 6 ++++++
>>> mm/memcontrol.c | 6 +++++-
>>> 2 files changed, 11 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>>> index 0e8907957227..c960fd49c3e8 100644
>>> --- a/include/linux/memcontrol.h
>>> +++ b/include/linux/memcontrol.h
>>> @@ -804,6 +804,12 @@ static inline void obj_cgroup_get(struct obj_cgroup *objcg)
>>> percpu_ref_get(&objcg->refcnt);
>>> }
>>>
>>> +static inline void obj_cgroup_get_many(struct obj_cgroup *objcg,
>>> + unsigned long nr)
>>> +{
>>> + percpu_ref_get_many(&objcg->refcnt, nr);
>>> +}
>>> +
>>> static inline void obj_cgroup_put(struct obj_cgroup *objcg)
>>> {
>>> percpu_ref_put(&objcg->refcnt);
>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>>> index c0b83a396299..64ada9e650a5 100644
>>> --- a/mm/memcontrol.c
>>> +++ b/mm/memcontrol.c
>>> @@ -3133,7 +3133,11 @@ void split_page_memcg(struct page *head, unsigned int nr)
>>>
>>> for (i = 1; i < nr; i++)
>>> head[i].memcg_data = head->memcg_data;
>>> - css_get_many(&memcg->css, nr - 1);
>>> +
>>> + if (PageMemcgKmem(head))
>>> + obj_cgroup_get_many(__page_objcg(head), nr - 1);
>>> + else
>>> + css_get_many(&memcg->css, nr - 1);
>>> }
>>>
>>> #ifdef CONFIG_MEMCG_SWAP
>>>
>>
> .
>
