[PATCH v2 2/2] cpufreq: Pass the policy to cpufreq_driver->adjust_perf()

[K Prateek Nayak <kprateek.nayak@amd.com>]

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.

Reported-by: Bert Karwatzki <spasswolf@web.de>
Closes:https://lore.kernel.org/all/20250731092316.3191-1-spasswolf@web.de/ [1]
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
Changelog rfc v1..v2:

o Updated the kdoc comment above cpufreq_driver_adjust_perf() to
  reflect that cpufreq_policy is passed as an argument now instead of
  the Target CPU. (kernel test robot)

o Added "Reported-by:" and "Closes:" tags. (Mario)

o Collected tags from v1. (Thank you Viresh)
---
 drivers/cpufreq/amd-pstate.c     | 3 +--
 drivers/cpufreq/cpufreq.c        | 6 +++---
 drivers/cpufreq/intel_pstate.c   | 4 ++--
 include/linux/cpufreq.h          | 4 ++--
 kernel/sched/cpufreq_schedutil.c | 5 +++--
 5 files changed, 11 insertions(+), 11 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..28b82c2eb7b3 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2225,7 +2225,7 @@ EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch);
 
 /**
  * cpufreq_driver_adjust_perf - Adjust CPU performance level in one go.
- * @cpu: Target CPU.
+ * @policy: cpufreq policy of the target CPU.
  * @min_perf: Minimum (required) performance level (units of @capacity).
  * @target_perf: Target (desired) performance level (units of @capacity).
  * @capacity: Capacity of the target CPU.
@@ -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)
-- 
2.34.1