From: Mike Kravetz <mike.kravetz@oracle.com>
To: Muchun Song <songmuchun@bytedance.com>,
Shakeel Butt <shakeelb@google.com>,
Mina Almasry <almasrymina@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Shuah Khan <shuah@kernel.org>, Miaohe Lin <linmiaohe@huawei.com>,
Oscar Salvador <osalvador@suse.de>,
Michal Hocko <mhocko@suse.com>,
David Rientjes <rientjes@google.com>, Jue Wang <juew@google.com>,
Yang Yao <ygyao@google.com>, Joanna Li <joannali@google.com>,
Cannon Matthews <cannonmatthews@google.com>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v6] hugetlb: Add hugetlb.*.numa_stat file
Date: Mon, 15 Nov 2021 10:22:03 -0800 [thread overview]
Message-ID: <6887a91a-9ec8-e06e-4507-b2dff701a147@oracle.com> (raw)
In-Reply-To: <CAMZfGtWJGqbji3OexrGi-uuZ6_LzdUs0q9Vd66SwH93_nfLJLA@mail.gmail.com>
Subject: Re: [PATCH v6] hugetlb: Add hugetlb.*.numa_stat file
To: Muchun Song <songmuchun@bytedance.com>, Shakeel Butt <shakeelb@google.com>, Mina Almasry <almasrymina@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Shuah Khan <shuah@kernel.org>, Miaohe Lin <linmiaohe@huawei.com>, Oscar Salvador <osalvador@suse.de>, Michal Hocko <mhocko@suse.com>, David Rientjes <rientjes@google.com>, Jue Wang <juew@google.com>, Yang Yao <ygyao@google.com>, Joanna Li <joannali@google.com>, Cannon Matthews <cannonmatthews@google.com>, Linux Memory Management List <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
Bcc:
-=-=-=-=-=-=-=-=-=# Don't remove this line #=-=-=-=-=-=-=-=-=-
On 11/14/21 5:43 AM, Muchun Song wrote:
> On Sun, Nov 14, 2021 at 3:15 AM Shakeel Butt <shakeelb@google.com> wrote:
>> On Sat, Nov 13, 2021 at 6:48 AM Mina Almasry <almasrymina@google.com> wrote:
>>> On Fri, Nov 12, 2021 at 6:45 PM Muchun Song <songmuchun@bytedance.com> wrote:
>>>> On Sat, Nov 13, 2021 at 7:36 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>> We have following options:
>>
>> 1) Use atomic type for usage.
>> 2) Use "unsigned long" for usage along with WRITE_ONCE/READ_ONCE.
>> 3) Use hugetlb_lock for hugetlb_cgroup_read_numa_stat as well.
>>
>> All options are valid but we would like to avoid (3).
>>
>> What if we use "unsigned long" type but without READ_ONCE/WRITE_ONCE.
>> The potential issues with that are KCSAN will report this as race and
>> possible garbage value on archs which do not support atomic writes to
>> unsigned long.
>
> At least I totally agree with you. Thanks for your detailed explanation.
>
Thanks everyone. This makes sense.
However, I should note that this same situation (updates to unsigned
long variables under lock and reads of the the same variable without
lock or READ/WRITE_ONCE) exists in hugetlb sysfs files today. Not
suggesting that this makes it OK to ignore the potential issue. Just
wanted to point this out.
--
Mike Kravetz
next prev parent reply other threads:[~2021-11-15 18:22 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 1:50 Mina Almasry
2021-11-11 2:04 ` Shakeel Butt
2021-11-11 2:36 ` Muchun Song
2021-11-11 2:59 ` Shakeel Butt
2021-11-12 23:36 ` Mike Kravetz
2021-11-13 2:44 ` Muchun Song
2021-11-13 14:48 ` Mina Almasry
2021-11-13 19:15 ` Shakeel Butt
2021-11-14 13:43 ` Muchun Song
2021-11-15 18:22 ` Mike Kravetz [this message]
2021-11-15 18:55 ` Mina Almasry
2021-11-15 19:59 ` Shakeel Butt
2021-11-16 12:04 ` Marco Elver
2021-11-16 20:48 ` Mina Almasry
2021-11-16 20:59 ` Shakeel Butt
2021-11-16 21:47 ` Marco Elver
2021-11-16 21:53 ` Mina Almasry
2021-11-17 5:54 ` Muchun Song
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