linux-kernel - Re: [PATCH 3/3] PM: s2idle: Fully block the system from entering s2idle when cpuidle isn't supported

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Date:   Mon, 27 Mar 2023 19:43:02 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kazuki H <kazukih0205@...il.com>
Cc:     linux-pm@...r.kernel.org, Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] PM: s2idle: Fully block the system from entering
 s2idle when cpuidle isn't supported

On Thu, Mar 16, 2023 at 8:49 AM Kazuki H <kazukih0205@...il.com> wrote:
>
> s2idle isn't supported on platforms that don't support cpuidle as of
> 31a3409065d1 ("cpuidle / sleep: Do sanity checks in cpuidle_enter_freeze()
> too").

This simply isn't correct.

As of the above commit, s2idle was still supported without cpuidle as
long as arch_cpu_idle() worked.

> There is a check in the cpuidle subsystem which would prevent the
> system from entering s2idle. However, there is nothing in the suspend
> framework which prevents this, which can cause the suspend subsystem to
> think that the machine is entering s2idle while the cpuidle subsystem is
> not, which can completely break the system.
>
> Block the machine from entering s2idle when cpuidle isn't supported in
> the suspend subsystem as well.

First, please explain why the cpuidle_not_available() check in
cpuidle_idle_call() is not sufficient to avoid the breakage.

> Link: https://lore.kernel.org/all/20230204152747.drte4uitljzngdt6@kazuki-mac
> Fixes: 31a3409065d1 ("cpuidle / sleep: Do sanity checks in cpuidle_enter_freeze() too")
> Signed-off-by: Kazuki H <kazukih0205@...il.com>
> ---
>  kernel/power/main.c    | 12 +++++++++---
>  kernel/power/suspend.c |  5 +++++
>  2 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/power/main.c b/kernel/power/main.c
> index 31ec4a9b9d70..b14765447989 100644
> --- a/kernel/power/main.c
> +++ b/kernel/power/main.c
> @@ -133,6 +133,8 @@ static ssize_t mem_sleep_show(struct kobject *kobj, struct kobj_attribute *attr,
>         for (i = PM_SUSPEND_MIN; i < PM_SUSPEND_MAX; i++) {
>                 if (i >= PM_SUSPEND_MEM && cxl_mem_active())
>                         continue;
> +               if (i == PM_SUSPEND_TO_IDLE && cpuidle_not_available())
> +                       continue;

Not really.

>                 if (mem_sleep_states[i]) {
>                         const char *label = mem_sleep_states[i];
>
> @@ -185,11 +187,15 @@ static ssize_t mem_sleep_store(struct kobject *kobj, struct kobj_attribute *attr
>         }
>
>         state = decode_suspend_state(buf, n);
> -       if (state < PM_SUSPEND_MAX && state > PM_SUSPEND_ON)
> +       if (state == PM_SUSPEND_TO_IDLE && cpuidle_not_available())

And same here.

> +               goto einval;
> +       if (state < PM_SUSPEND_MAX && state > PM_SUSPEND_ON) {
>                 mem_sleep_current = state;
> -       else
> -               error = -EINVAL;
> +               goto out;
> +       }
>
> + einval:
> +       error = -EINVAL;
>   out:
>         pm_autosleep_unlock();
>         return error ? error : n;
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index 3f436282547c..55ddf525aaaf 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -556,6 +556,11 @@ static int enter_state(suspend_state_t state)
>
>         trace_suspend_resume(TPS("suspend_enter"), state, true);
>         if (state == PM_SUSPEND_TO_IDLE) {
> +               if (cpuidle_not_available()) {
> +                       pr_warn("s2idle is unsupported when cpuidle is unavailable");
> +                       return -EINVAL;
> +               }
> +
>  #ifdef CONFIG_PM_DEBUG
>                 if (pm_test_level != TEST_NONE && pm_test_level <= TEST_CPUS) {
>                         pr_warn("Unsupported test mode for suspend to idle, please choose none/freezer/devices/platform.\n");
> --

Again, I need to understand what the problem is in the first place.