Re: [PATCH v3] cpufreq: schedutil: Serialize start against rate limit updates

[Rafael J. Wysocki (Intel)]

On Tue, Oct 13, 2026 at 5:43 AM Hui Su <sh_def@xxxxxxx> wrote:
>
> rate_limit_us_store() updates the tunable and freq_update_delay_ns under
> update_lock, but sugov_start() reads the tunable without it. Startup can
> therefore overwrite the new delay with one based on a stale value.
>
> Serialize the startup update with sysfs stores by taking update_lock in a
> schedutil-local wrapper.
>
> Fixes: 9bdcb44e391d ("cpufreq: schedutil: New governor based on scheduler utilization data")
> Reviewed-by: Zhongqiu Han <zhongqiu.han@xxxxxxxxxxxxxxxx>
> Signed-off-by: Hui Su <sh_def@xxxxxxx>
> ---
> Changes in v3:
> - Use a schedutil-local scoped wrapper and clarify the locking comment.
>
> v2: https://lore.kernel.org/lkml/20261007155820.3194105-1-sh_def@xxxxxxx/
> ---
>  kernel/sched/cpufreq_schedutil.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 49ccd6f1c185..1d0878dad4b0 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -73,6 +73,16 @@ static void sugov_update_rate_limit_us(struct sugov_policy *sg_policy)
>                 (s64)sg_policy->tunables->rate_limit_us * NSEC_PER_USEC;
>  }
>
> +static void sugov_update_rate_limit_us_sync(struct sugov_policy *sg_policy)
> +{
> +       /*
> +        * Serialize with rate_limit_us_store() to prevent this path from
> +        * overwriting the new delay with one based on an old tunable value.
> +        */
> +       guard(mutex)(&sg_policy->tunables->attr_set.update_lock);
> +       sugov_update_rate_limit_us(sg_policy);
> +}
> +
>  static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
>  {
>         s64 delta_ns;
> @@ -861,7 +871,7 @@ static int sugov_start(struct cpufreq_policy *policy)
>         void (*uu)(struct update_util_data *data, u64 time, unsigned int flags);
>         unsigned int cpu;
>
> -       sugov_update_rate_limit_us(sg_policy);
> +       sugov_update_rate_limit_us_sync(sg_policy);
>         sg_policy->last_freq_update_time        = 0;
>         sg_policy->next_freq                    = 0;
>         sg_policy->work_in_progress             = false;
>

Applied as 7.4 material, thanks!