Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH 5/5] mm, memcg: always call __mod_node_page_state() with
 preempt disabled
To:     Shakeel Butt <shakeelb@google.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>
References: <20210729125755.16871-1-linmiaohe@huawei.com>
 <20210729125755.16871-6-linmiaohe@huawei.com>
 <CALvZod6n1EwcyLTi=Eb8t=NVVPLRh9=Ng=VJ93pQyCRkOcLo9Q@mail.gmail.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <29c4bb2a-ceaf-6c8b-c222-38b30460780f@huawei.com>
Date:   Fri, 30 Jul 2021 09:52:20 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.0
MIME-Version: 1.0
In-Reply-To: <CALvZod6n1EwcyLTi=Eb8t=NVVPLRh9=Ng=VJ93pQyCRkOcLo9Q@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2021/7/29 22:39, Shakeel Butt wrote:
> 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().
> 

I thought it's used to protect __mod_node_page_state(). Looks somewhat confusing for me.
Many thanks for pointing this out!

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