Re: [PATCH 6.14.y and others] cpufreq: Reference count policy in cpufreq_update_limits()

["Wysocki, Rafael J" <rafael.j.wysocki@intel.com>]

On 4/18/2025 4:15 AM, Marek Marczykowski-Górecki wrote:
> From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
>
> Since acpi_processor_notify() can be called before registering a cpufreq
> driver or even in cases when a cpufreq driver is not registered at all,
> cpufreq_update_limits() needs to check if a cpufreq driver is present
> and prevent it from being unregistered.
>
> For this purpose, make it call cpufreq_cpu_get() to obtain a cpufreq
> policy pointer for the given CPU and reference count the corresponding
> policy object, if present.
>
> Fixes: 5a25e3f7cc53 ("cpufreq: intel_pstate: Driver-specific handling of _PPC updates")
> Closes: https://lore.kernel.org/linux-acpi/Z-ShAR59cTow0KcR@mail-itl
> Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
> Cc: All applicable <stable@vger.kernel.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
> Link: https://patch.msgid.link/1928789.tdWV9SEqCh@rjwysocki.net
> (cherry picked from commit 9e4e249018d208678888bdf22f6b652728106528)
> [do not use __free(cpufreq_cpu_put) in a backport]
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
> ---
> This patch is applicable to other stable branches too.

Thanks a lot for taking care of backporting it!


> ---
>   drivers/cpufreq/cpufreq.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 30ffbddc7ece..934e0e19824c 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2762,10 +2762,18 @@ EXPORT_SYMBOL(cpufreq_update_policy);
>    */
>   void cpufreq_update_limits(unsigned int cpu)
>   {
> +	struct cpufreq_policy *policy;
> +
> +	policy = cpufreq_cpu_get(cpu);
> +	if (!policy)
> +		return;
> +
>   	if (cpufreq_driver->update_limits)
>   		cpufreq_driver->update_limits(cpu);
>   	else
>   		cpufreq_update_policy(cpu);
> +
> +	cpufreq_cpu_put(policy);
>   }
>   EXPORT_SYMBOL_GPL(cpufreq_update_limits);
>