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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Wed, 13 Apr 2022 20:48:20 +0200
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Subject: Re: [PATCH v7 03/20] reboot: Print error message if restart handler
 has duplicated priority
To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>
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On Tue, Apr 12, 2022 at 1:39 AM Dmitry Osipenko
<dmitry.osipenko@collabora.com> wrote:
>
> Add sanity check which ensures that there are no two restart handlers
> registered using the same priority. This requirement will become mandatory
> once all drivers will be converted to the new API and such errors will be
> fixed.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

The first two patches in the series are fine with me and there's only
one minor nit regarding this one (below).

> ---
>  kernel/reboot.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index ed4e6dfb7d44..acdae4e95061 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -182,6 +182,21 @@ static ATOMIC_NOTIFIER_HEAD(restart_handler_list);
>   */
>  int register_restart_handler(struct notifier_block *nb)
>  {
> +       int ret;
> +
> +       ret = atomic_notifier_chain_register_unique_prio(&restart_handler_list, nb);
> +       if (ret != -EBUSY)
> +               return ret;
> +
> +       /*
> +        * Handler must have unique priority. Otherwise call order is
> +        * determined by registration order, which is unreliable.
> +        *
> +        * This requirement will become mandatory once all drivers
> +        * will be converted to use new sys-off API.
> +        */
> +       pr_err("failed to register restart handler using unique priority\n");

I would use pr_info() here, because this is not a substantial error AFAICS.

> +
>         return atomic_notifier_chain_register(&restart_handler_list, nb);
>  }
>  EXPORT_SYMBOL(register_restart_handler);
> --