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From:   Shakeel Butt <shakeelb@google.com>
Date:   Thu, 29 Jul 2021 07:39:08 -0700
Message-ID: <CALvZod6n1EwcyLTi=Eb8t=NVVPLRh9=Ng=VJ93pQyCRkOcLo9Q@mail.gmail.com>
Subject: Re: [PATCH 5/5] mm, memcg: always call __mod_node_page_state() with
 preempt disabled
To:     Miaohe Lin <linmiaohe@huawei.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>,
        Matthew Wilcox <willy@infradead.org>, alexs@kernel.org,
        Wei Yang <richard.weiyang@gmail.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Cgroups <cgroups@vger.kernel.org>
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On Thu, Jul 29, 2021 at 5:58 AM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> We should always ensure __mod_node_page_state() is called with preempt
> disabled or percpu ops may manipulate the wrong cpu when preempt happened.
>
> Fixes: b4e0b68fbd9d ("mm: memcontrol: use obj_cgroup APIs to charge kmem pages")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 70a32174e7c4..616d1a72ece3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -697,8 +697,8 @@ void __mod_lruvec_page_state(struct page *page, enum node_stat_item idx,
>         memcg = page_memcg(head);
>         /* Untracked pages have no memcg, no lruvec. Update only the node */
>         if (!memcg) {
> -               rcu_read_unlock();
>                 __mod_node_page_state(pgdat, idx, val);
> +               rcu_read_unlock();

This rcu is for page_memcg. The preemption and interrupts are disabled
across __mod_lruvec_page_state().

>                 return;
>         }
>
> --
> 2.23.0
>