linux-kernel - Re: [PATCH] cpufreq: Initialize cpufreq-based invariance before subsys

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Message-ID: <CAJZ5v0hWTtQWVJ1VkC9AH4jtCLWFhak0adaiE0Yq=ZwVo+fscA@mail.gmail.com>
Date: Sat, 20 Sep 2025 13:03:39 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Christian Loehle <christian.loehle@....com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-pm <linux-pm@...r.kernel.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>, 
	"zhenglifeng (A)" <zhenglifeng1@...wei.com>
Subject: Re: [PATCH] cpufreq: Initialize cpufreq-based invariance before subsys

On Thu, Sep 18, 2025 at 12:15 PM Christian Loehle
<christian.loehle@....com> wrote:
>
> commit 2a6c72738706 ("cpufreq: Initialize cpufreq-based
> frequency-invariance later") postponed the frequency invariance
> initialization to avoid disabling it in the error case.
> This isn't locking safe, instead move the initialization up before
> the subsys interface is registered (which will rebuild the
> sched_domains) and add the corresponding disable on the error path.
>
> Observed lockdep without this patch:
> [    0.989686] ======================================================
> [    0.989688] WARNING: possible circular locking dependency detected
> [    0.989690] 6.17.0-rc4-cix-build+ #31 Tainted: G S
> [    0.989691] ------------------------------------------------------
> [    0.989692] swapper/0/1 is trying to acquire lock:
> [    0.989693] ffff800082ada7f8 (sched_energy_mutex){+.+.}-{4:4}, at: rebuild_sched_domains_energy+0x30/0x58
> [    0.989705]
>                but task is already holding lock:
> [    0.989706] ffff000088c89bc8 (&policy->rwsem){+.+.}-{4:4}, at: cpufreq_online+0x7f8/0xbe0
> [    0.989713]
>                which lock already depends on the new lock.
>
> Fixes: 2a6c72738706 ("cpufreq: Initialize cpufreq-based frequency-invariance later")
> Signed-off-by: Christian Loehle <christian.loehle@....com>
> ---
>  drivers/cpufreq/cpufreq.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index fc7eace8b65b..58e3839a2140 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2953,6 +2953,15 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
>                         goto err_null_driver;
>         }
>
> +       /*
> +        * Mark support for the scheduler's frequency invariance engine for
> +        * drivers that implement target(), target_index() or fast_switch().
> +        */
> +       if (!cpufreq_driver->setpolicy) {
> +               static_branch_enable_cpuslocked(&cpufreq_freq_invariance);
> +               pr_debug("cpufreq: supports frequency invariance\n");
> +       }
> +
>         ret = subsys_interface_register(&cpufreq_interface);
>         if (ret)
>                 goto err_boost_unreg;
> @@ -2974,21 +2983,14 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
>         hp_online = ret;
>         ret = 0;
>
> -       /*
> -        * Mark support for the scheduler's frequency invariance engine for
> -        * drivers that implement target(), target_index() or fast_switch().
> -        */
> -       if (!cpufreq_driver->setpolicy) {
> -               static_branch_enable_cpuslocked(&cpufreq_freq_invariance);
> -               pr_debug("supports frequency invariance");
> -       }
> -
>         pr_debug("driver %s up and running\n", driver_data->name);
>         goto out;
>
>  err_if_unreg:
>         subsys_interface_unregister(&cpufreq_interface);
>  err_boost_unreg:
> +       if (!cpufreq_driver->setpolicy)
> +               static_branch_disable_cpuslocked(&cpufreq_freq_invariance);
>         remove_boost_sysfs_file();
>  err_null_driver:
>         write_lock_irqsave(&cpufreq_driver_lock, flags);
> --

Applied as 6.17-rc material, thanks!