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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Qian Cai <quic_qiancai@quicinc.com>
Cc:     Miaohe Lin <linmiaohe@huawei.com>, <akpm@linux-foundation.org>,
        <david@redhat.com>, <songmuchun@bytedance.com>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/2] mm/swapfile: fix possible data races of inuse_pages
References: <20220625093346.48894-1-linmiaohe@huawei.com>
        <20220625093346.48894-2-linmiaohe@huawei.com> <Yrml4mB3sa5fZVJa@qian>
        <fe3c4834-71a6-7867-2108-eca43fde62fc@huawei.com>
        <Yrm05NQs5+tCZawR@qian>
Date:   Tue, 28 Jun 2022 09:56:58 +0800
In-Reply-To: <Yrm05NQs5+tCZawR@qian> (Qian Cai's message of "Mon, 27 Jun 2022
        09:47:16 -0400")
Message-ID: <874k057dp1.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Qian Cai <quic_qiancai@quicinc.com> writes:

> On Mon, Jun 27, 2022 at 09:27:43PM +0800, Miaohe Lin wrote:
>> On 2022/6/27 20:43, Qian Cai wrote:
>> > On Sat, Jun 25, 2022 at 05:33:45PM +0800, Miaohe Lin wrote:
>> >> si->inuse_pages could still be accessed concurrently now. The plain reads
>> >> outside si->lock critical section, i.e. swap_show and si_swapinfo, which
>> >> results in data races. READ_ONCE and WRITE_ONCE is used to fix such data
>> >> races. Note these data races should be ok because they're just used for
>> >> showing swap info.
>> > 
>> > Was this found by kcsan? If so, it would be useful to record the exact
>> > kscan report in the commit message.
>> 
>> Sorry, it's found via code inspection.
>
> Well, if we are going to do a WRITE_ONCE() in those places just for
> documentation purpose now, I think we will need to fix all places in the mm
> subsystem to be consistent.

We have already done this in swapfile.c, please search "WRITE_ONCE"
in that file.

Best Regards,
Huang, Ying