linux-kernel - Re: [RFC PATCH v4 1/8] cpuidle: Do not return from cpuidle_play

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Message-ID: <CAJZ5v0hG4gJEZW-53Ps+AUPdkZCubH2Px35BmN1_goRTMb9EeA@mail.gmail.com>
Date: Mon, 25 Nov 2024 14:26:08 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	rafael.j.wysocki@...el.com, len.brown@...el.com, 
	artem.bityutskiy@...ux.intel.com, dave.hansen@...ux.intel.com, 
	peterz@...radead.org, tglx@...utronix.de, gautham.shenoy@....com
Subject: Re: [RFC PATCH v4 1/8] cpuidle: Do not return from
 cpuidle_play_dead() on callback failures

On Mon, Nov 25, 2024 at 2:20 PM Patryk Wlazlyn
<patryk.wlazlyn@...ux.intel.com> 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
> Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>

This one and the [2/2] are in the mainline as of today, no need to resend them.

> ---
>  drivers/cpuidle/cpuidle.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 06ace16f9e71..0835da449db8 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/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;
>  }
>
> --
> 2.47.0
>
>