Re: [RFC PATCH 2/2] cpufreq: Pass the policy to cpufreq_driver->adjust_perf()

["Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>]

On 1/6/2026 1:36 AM, K Prateek Nayak wrote:
> cpufreq_cpu_get() can sleep on PREEMPT_RT in presence of concurrent
> writer(s), however amd-pstate depends on fetching the cpudata via the
> policy's driver data which necessitates grabbing the reference.
> 
> Since schedutil governor can call "cpufreq_driver->update_perf()"
> during sched_tick/enqueue/dequeue with rq_lock held and IRQs disabled,
> fetching the policy object using the cpufreq_cpu_get() helper in the
> scheduler fast-path leads to "BUG: scheduling while atomic" on
> PREEMPT_RT [1].
> 
> Pass the cached cpufreq policy object in sg_policy to the update_perf()
> instead of just the CPU. The CPU can be inferred using "policy->cpu".
> 
> The lifetime of cpufreq_policy object outlasts that of the governor and
> the cpufreq driver (allocated when the CPU is onlined and only reclaimed
> when the CPU is offlined / the CPU device is removed) which makes it
> safe to be referenced throughout the governor's lifetime.
> 
> Link: https://lore.kernel.org/all/20250731092316.3191-1-spasswolf@web.de/ [1]

I think you should have these tags instead:
Reported-by: Bert Karwatzki <spasswolf@web.de>
Closes:https://lore.kernel.org/all/20250731092316.3191-1-spasswolf@web.de/ 
[1]

> Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
> ---
>   drivers/cpufreq/amd-pstate.c     | 3 +--
>   drivers/cpufreq/cpufreq.c        | 4 ++--
>   drivers/cpufreq/intel_pstate.c   | 4 ++--
>   include/linux/cpufreq.h          | 4 ++--
>   kernel/sched/cpufreq_schedutil.c | 5 +++--
>   5 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 5818a92d96b9..455e58a9b738 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -697,13 +697,12 @@ static unsigned int amd_pstate_fast_switch(struct cpufreq_policy *policy,
>   	return policy->cur;
>   }
>   
> -static void amd_pstate_adjust_perf(unsigned int cpu,
> +static void amd_pstate_adjust_perf(struct cpufreq_policy *policy,
>   				   unsigned long _min_perf,
>   				   unsigned long target_perf,
>   				   unsigned long capacity)
>   {
>   	u8 max_perf, min_perf, des_perf, cap_perf;
> -	struct cpufreq_policy *policy __free(put_cpufreq_policy) = cpufreq_cpu_get(cpu);
>   	struct amd_cpudata *cpudata;
>   	union perf_cached perf;
>   
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 50dde2980f1b..8bdc8f9b8d86 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2244,12 +2244,12 @@ EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch);
>    * parallel with either ->target() or ->target_index() or ->fast_switch() for
>    * the same CPU.
>    */
> -void cpufreq_driver_adjust_perf(unsigned int cpu,
> +void cpufreq_driver_adjust_perf(struct cpufreq_policy *policy,
>   				 unsigned long min_perf,
>   				 unsigned long target_perf,
>   				 unsigned long capacity)
>   {
> -	cpufreq_driver->adjust_perf(cpu, min_perf, target_perf, capacity);
> +	cpufreq_driver->adjust_perf(policy, min_perf, target_perf, capacity);
>   }
>   
>   /**
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index ec4abe374573..8d25f0f2925c 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -3237,12 +3237,12 @@ static unsigned int intel_cpufreq_fast_switch(struct cpufreq_policy *policy,
>   	return target_pstate * cpu->pstate.scaling;
>   }
>   
> -static void intel_cpufreq_adjust_perf(unsigned int cpunum,
> +static void intel_cpufreq_adjust_perf(struct cpufreq_policy *policy,
>   				      unsigned long min_perf,
>   				      unsigned long target_perf,
>   				      unsigned long capacity)
>   {
> -	struct cpudata *cpu = all_cpu_data[cpunum];
> +	struct cpudata *cpu = all_cpu_data[policy->cpu];
>   	u64 hwp_cap = READ_ONCE(cpu->hwp_cap_cached);
>   	int old_pstate = cpu->pstate.current_pstate;
>   	int cap_pstate, min_pstate, max_pstate, target_pstate;
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index 0465d1e6f72a..fd26b3a4aa28 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -367,7 +367,7 @@ struct cpufreq_driver {
>   	 * conditions) scale invariance can be disabled, which causes the
>   	 * schedutil governor to fall back to the latter.
>   	 */
> -	void		(*adjust_perf)(unsigned int cpu,
> +	void		(*adjust_perf)(struct cpufreq_policy *policy,
>   				       unsigned long min_perf,
>   				       unsigned long target_perf,
>   				       unsigned long capacity);
> @@ -612,7 +612,7 @@ struct cpufreq_governor {
>   /* Pass a target to the cpufreq driver */
>   unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
>   					unsigned int target_freq);
> -void cpufreq_driver_adjust_perf(unsigned int cpu,
> +void cpufreq_driver_adjust_perf(struct cpufreq_policy *policy,
>   				unsigned long min_perf,
>   				unsigned long target_perf,
>   				unsigned long capacity);
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 0ab5f9d4bc59..307f3076635e 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -461,6 +461,7 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
>   				     unsigned int flags)
>   {
>   	struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu, update_util);
> +	struct sugov_policy *sg_policy = sg_cpu->sg_policy;
>   	unsigned long prev_util = sg_cpu->util;
>   	unsigned long max_cap;
>   
> @@ -482,10 +483,10 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
>   	if (sugov_hold_freq(sg_cpu) && sg_cpu->util < prev_util)
>   		sg_cpu->util = prev_util;
>   
> -	cpufreq_driver_adjust_perf(sg_cpu->cpu, sg_cpu->bw_min,
> +	cpufreq_driver_adjust_perf(sg_policy->policy, sg_cpu->bw_min,
>   				   sg_cpu->util, max_cap);
>   
> -	sg_cpu->sg_policy->last_freq_update_time = time;
> +	sg_policy->last_freq_update_time = time;
>   }
>   
>   static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)