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To:     Muchun Song <songmuchun@bytedance.com>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        Yang Shi <shy828301@gmail.com>,
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        Shakeel Butt <shakeelb@google.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Xiongchun Duan <duanxiongchun@bytedance.com>
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From:   Christian Borntraeger <borntraeger@de.ibm.com>
Message-ID: <179f84ad-7b98-4bc5-f895-c19faabbb311@de.ibm.com>
Date:   Wed, 31 Mar 2021 08:22:41 +0200
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Subject: RE: kernel warning percpu ref in obj_cgroup_release
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On 30.03.21 18:25, Muchun Song wrote:
> On Tue, Mar 30, 2021 at 11:10 PM Christian Borntraeger
> <borntraeger@de.ibm.com> wrote:
>>
>>
>> On 30.03.21 15:49, Muchun Song wrote:
>>> On Tue, Mar 30, 2021 at 9:27 PM Christian Borntraeger
>>> <borntraeger@de.ibm.com> wrote:
>>>>
>>>> So bisect shows this for belows warning:
>>>
>>> Thanks for your effort on this. Can you share your config?
>>
>> attached (but its s390x) for next-20210330
> 
> Thanks. Can you apply the following patch and help me test?
> Very Thanks.
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 7fdc92e1983e..579408e4d46f 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -793,6 +793,12 @@ 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..1634dba1044c 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3133,7 +3133,10 @@ 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
> 

This one seems to do the trick, I can no longer see the warning.