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

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Message-ID: <Yrm05NQs5+tCZawR@qian>
Date:   Mon, 27 Jun 2022 09:47:16 -0400
From:   Qian Cai <quic_qiancai@...cinc.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
CC:     <akpm@...ux-foundation.org>, <david@...hat.com>,
        <ying.huang@...el.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

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.