linux-kernel - Re: [PATCH v1] cpuidle: Do not return from cpuidle_play

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Message-ID: <20241115101427.GA22801@noisy.programming.kicks-ass.net>
Date: Fri, 15 Nov 2024 11:14:27 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	x86 Maintainers <x86@...nel.org>,
	Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>,
	"Gautham R. Shenoy" <gautham.shenoy@....com>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
	Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v1] cpuidle: Do not return from cpuidle_play_dead() on
 callback failures

On Thu, Nov 14, 2024 at 06:46:20PM +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.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpuidle/cpuidle.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> Index: linux-pm/drivers/cpuidle/cpuidle.c
> ===================================================================
> --- linux-pm.orig/drivers/cpuidle/cpuidle.c
> +++ linux-pm/drivers/cpuidle/cpuidle.c
> @@ -70,9 +70,10 @@ int cpuidle_play_dead(void)
>  		return -ENODEV;
>  
>  	/* Find lowest-power state that supports long-term idle */
> -	for (i = drv->state_count - 1; i >= 0; i--)
> -		if (drv->states[i].enter_dead)
> -			return drv->states[i].enter_dead(dev, i);
> +	for (i = drv->state_count - 1; i >= 0; i--) {
> +		if (drv->states[i].enter_dead && !drv->states[i].enter_dead(dev, i))
> +			return 0;
> +	}

Hmm, strictly speaking there is no 'success' return from play_dead(). On
success, the CPU is dead :-)