linux-kernel - Re: [PATCH v3 1/2] mm/swapfile: fix possible data races of inuse

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Date:   Tue, 28 Jun 2022 09:56:58 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     Miaohe Lin <linmiaohe@...wei.com>, <akpm@...ux-foundation.org>,
        <david@...hat.com>, <songmuchun@...edance.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] mm/swapfile: fix possible data races of inuse_pages

Qian Cai <quic_qiancai@...cinc.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