linux-kernel - Re: [PATCH v2 1/2] cpuidle: Do not return from cpuidle_play

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Message-ID: <Zzya+PIRDlKrd9Ed@BLRRASHENOY1.amd.com>
Date: Tue, 19 Nov 2024 19:34:40 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	x86 Maintainers <x86@...nel.org>,
	Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] cpuidle: Do not return from cpuidle_play_dead()
 on callback failures

Hello Rafael,

On Fri, Nov 15, 2024 at 09:58:31PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> If the :enter_dead() idle state callback fails for a certain state,
> there may be still a shallower state for which it will work.
> 
> Because the only caller of cpuidle_play_dead(), native_play_dead(),
> falls back to hlt_play_dead() if it returns an error, it should
> better try all of the idle states for which :enter_dead() is present
> before failing, so change it accordingly.
> 
> Also notice that the :enter_dead() state callback is not expected
> to return on success (the CPU should be "dead" then), so make
> cpuidle_play_dead() ignore its return value.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Reviewed-by: Mario Limonciello <mario.limonciello@....com>
> Tested-by: Mario Limonciello <mario.limonciello@....com> # 6.12-rc7

Thanks for fixing this.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>

--
Thanks and Regards
gautham.
> ---
> 
> v1 -> v2:
>    * Make cpuidle_play_dead() never return 0.
>    * Add tags from Mario (I have added them because the change of the patch
>      should not make a practical difference, but if you want them to be
>      dropped, please let me know).
> 
> ---
>  drivers/cpuidle/cpuidle.c |   10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> Index: linux-pm/drivers/cpuidle/cpuidle.c
> ===================================================================
> --- linux-pm.orig/drivers/cpuidle/cpuidle.c
> +++ linux-pm/drivers/cpuidle/cpuidle.c
> @@ -69,11 +69,15 @@ int cpuidle_play_dead(void)
>  	if (!drv)
>  		return -ENODEV;
>  
> -	/* Find lowest-power state that supports long-term idle */
> -	for (i = drv->state_count - 1; i >= 0; i--)
> +	for (i = drv->state_count - 1; i >= 0; i--) {
>  		if (drv->states[i].enter_dead)
> -			return drv->states[i].enter_dead(dev, i);
> +			drv->states[i].enter_dead(dev, i);
> +	}
>  
> +	/*
> +	 * If :enter_dead() is successful, it will never return, so reaching
> +	 * here means that all of them failed above or were not present.
> +	 */
>  	return -ENODEV;
>  }
>  
> 
> 
>