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From: Song Liu <song@kernel.org>
Date: Tue, 27 Feb 2024 14:28:00 -0800
Message-ID: <CAPhsuW5u1SHCjw-0EUEvOp9-+nyh3s67Nio=OR=P1ftRTe33gA@mail.gmail.com>
Subject: Re: [PATCH v4] md/raid5: fix atomicity violation in raid5_cache_count
To: Yu Kuai <yukuai1@huaweicloud.com>
Cc: Gui-Dong Han <2045gemini@gmail.com>, linux-raid@vger.kernel.org, 
	linux-kernel@vger.kernel.org, baijiaju1990@outlook.com, 
	stable@vger.kernel.org, "yukuai (C)" <yukuai3@huawei.com>
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On Thu, Feb 1, 2024 at 11:11=E2=80=AFPM Yu Kuai <yukuai1@huaweicloud.com> w=
rote:
>
> Hi,
>
> =E5=9C=A8 2024/01/30 15:37, Song Liu =E5=86=99=E9=81=93:
> > On Thu, Jan 11, 2024 at 11:10=E2=80=AFPM Gui-Dong Han <2045gemini@gmail=
com> wrote:
> >>
> > [...]
> >>
> >>          raid5_release_stripe(sh);
> >> -       conf->max_nr_stripes++;
> >> +       WRITE_ONCE(conf->max_nr_stripes, conf->max_nr_stripes + 1);
> >
> > This is weird. We are reading max_nr_stripes without READ_ONCE.
>
> We don't need READ_ONCE() here because writers are protected by
> 'cache_size_mutex', there are no concurrent writers, it's safe to
> read 'max_nr_stripes' directly.

OK, that makes sense. Applied to md-6.9.

Thanks,
Song