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References: <20230310073855.1337560-1-yukuai1@huaweicloud.com> <20230310073855.1337560-3-yukuai1@huaweicloud.com>
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From:   Song Liu <song@kernel.org>
Date:   Mon, 13 Mar 2023 15:24:41 -0700
Message-ID: <CAPhsuW6eYdWgGyZjnXcT4yY4y-pcy3eEzc8uanStNz9aEGeGLg@mail.gmail.com>
Subject: Re: [PATCH v2 2/6] md: fix soft lockup in status_resync
To:     Yu Kuai <yukuai1@huaweicloud.com>
Cc:     guoqing.jiang@linux.dev, jgq516@gmail.com, neilb@suse.de,
        shli@fb.com, lzhong@suse.com, linux-raid@vger.kernel.org,
        linux-kernel@vger.kernel.org, yukuai3@huawei.com,
        yi.zhang@huawei.com, yangerkun@huawei.com
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On Thu, Mar 9, 2023 at 11:39=E2=80=AFPM Yu Kuai <yukuai1@huaweicloud.com> w=
rote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> status_resync() will calculate 'curr_resync - recovery_active' to show
> user a progress bar like following:
>
> [=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D>........]  resync =3D 61.4%
>
> 'curr_resync' and 'recovery_active' is updated in md_do_sync(), and
> status_resync() can read them concurrently, hence it's possible that
> 'curr_resync - recovery_active' can overflow to a huge number. In this
> case status_resync() will be stuck in the loop to print a large amount
> of '=3D', which will end up soft lockup.
>
> Fix the problem by setting 'resync' to MD_RESYNC_ACTIVE in this case,
> this way resync in progress will be reported to user.
>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Looks good. Applied to md-next.

Thanks,
Song

> ---
>  drivers/md/md.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 546b1b81eb28..98970bbe32bf 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8009,16 +8009,16 @@ static int status_resync(struct seq_file *seq, st=
ruct mddev *mddev)
>         } else if (resync > max_sectors) {
>                 resync =3D max_sectors;
>         } else {
> -               resync -=3D atomic_read(&mddev->recovery_active);
> -               if (resync < MD_RESYNC_ACTIVE) {
> -                       /*
> -                        * Resync has started, but the subtraction has
> -                        * yielded one of the special values. Force it
> -                        * to active to ensure the status reports an
> -                        * active resync.
> -                        */
> +               res =3D atomic_read(&mddev->recovery_active);
> +               /*
> +                * Resync has started, but the subtraction has overflowed=
 or
> +                * yielded one of the special values. Force it to active =
to
> +                * ensure the status reports an active resync.
> +                */
> +               if (resync < res || resync - res < MD_RESYNC_ACTIVE)
>                         resync =3D MD_RESYNC_ACTIVE;
> -               }
> +               else
> +                       resync -=3D res;
>         }
>
>         if (resync =3D=3D MD_RESYNC_NONE) {
> --
> 2.31.1
>