linux-kernel - Re: [PATCH v4] md/raid5: fix atomicity violation in raid5_cache

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Message-ID: <CAPhsuW5u1SHCjw-0EUEvOp9-+nyh3s67Nio=OR=P1ftRTe33gA@mail.gmail.com>
Date: Tue, 27 Feb 2024 14:28:00 -0800
From: Song Liu <song@...nel.org>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: Gui-Dong Han <2045gemini@...il.com>, linux-raid@...r.kernel.org, 
	linux-kernel@...r.kernel.org, baijiaju1990@...look.com, 
	stable@...r.kernel.org, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v4] md/raid5: fix atomicity violation in raid5_cache_count

On Thu, Feb 1, 2024 at 11:11 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2024/01/30 15:37, Song Liu 写道:
> > On Thu, Jan 11, 2024 at 11:10 PM Gui-Dong Han <2045gemini@...ilcom> 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