linux-kernel - Re: [PATCH v1] kernel/reboot: Change registration order of legacy power-off handler

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Message-ID: <8735gjq365.fsf@mpe.ellerman.id.au>
Date:   Sun, 05 Jun 2022 12:01:22 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     linux-kernel@...r.kernel.org, <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v1] kernel/reboot: Change registration order of legacy
 power-off handler

Dmitry Osipenko <dmitry.osipenko@...labora.com> writes:
> We're unconditionally registering sys-off handler for the legacy
> pm_power_off() callback, this causes problem for platforms that don't
> use power-off handlers at all and should be halted. Now reboot syscall
> assumes that there is a power-off handler installed and tries to power
> off system instead of halting it.
>
> To fix the trouble, move the handler's registration to the reboot syscall
> and check the pm_power_off() presence.

I'm seeing a qemu virtual machine (ppce500) fail to power off using the
gpio-poweroff driver. I bisected it to this commit.

I think the problem is that the machine is going via kernel_power_off(),
not sys_reboot(), and so legacy_pm_power_off() has not been registered.

If I just put the core_initcall back then it works as before. Not sure
if that's a safe change in general though.

cheers



> Fixes: 0e2110d2e910 ("kernel/reboot: Add kernel_can_power_off()")
> Reported-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> ---
>  kernel/reboot.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index 0bdc64ecf4f6..a091145ee710 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -569,22 +569,6 @@ static int legacy_pm_power_off(struct sys_off_data *data)
>  	return NOTIFY_DONE;
>  }
>  
> -/*
> - * Register sys-off handlers for legacy PM callbacks. This allows legacy
> - * PM callbacks co-exist with the new sys-off API.
> - *
> - * TODO: Remove legacy handlers once all legacy PM users will be switched
> - *       to the sys-off based APIs.
> - */
> -static int __init legacy_pm_init(void)
> -{
> -	register_sys_off_handler(SYS_OFF_MODE_POWER_OFF, SYS_OFF_PRIO_DEFAULT,
> -				 legacy_pm_power_off, NULL);
> -
> -	return 0;
> -}
> -core_initcall(legacy_pm_init);
> -
>  static void do_kernel_power_off_prepare(void)
>  {
>  	blocking_notifier_call_chain(&power_off_prep_handler_list, 0, NULL);
> @@ -646,6 +630,7 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
>  		void __user *, arg)
>  {
>  	struct pid_namespace *pid_ns = task_active_pid_ns(current);
> +	struct sys_off_handler *sys_off = NULL;
>  	char buffer[256];
>  	int ret = 0;
>  
> @@ -670,6 +655,21 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
>  	if (ret)
>  		return ret;
>  
> +	/*
> +	 * Register sys-off handlers for legacy PM callback. This allows
> +	 * legacy PM callbacks temporary co-exist with the new sys-off API.
> +	 *
> +	 * TODO: Remove legacy handlers once all legacy PM users will be
> +	 *       switched to the sys-off based APIs.
> +	 */
> +	if (pm_power_off) {
> +		sys_off = register_sys_off_handler(SYS_OFF_MODE_POWER_OFF,
> +						   SYS_OFF_PRIO_DEFAULT,
> +						   legacy_pm_power_off, NULL);
> +		if (IS_ERR(sys_off))
> +			return PTR_ERR(sys_off);
> +	}
> +
>  	/* Instead of trying to make the power_off code look like
>  	 * halt when pm_power_off is not set do it the easy way.
>  	 */
> @@ -727,6 +727,7 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
>  		break;
>  	}
>  	mutex_unlock(&system_transition_mutex);
> +	unregister_sys_off_handler(sys_off);
>  	return ret;
>  }
>  
> -- 
> 2.35.3