* [PATCH v3 1/2] cpufreq/amd-pstate: Pass the policy to amd_pstate_update()
2026-01-16 6:32 [PATCH v3 0/2] cpufreq/amd-pstate: Prevent scheduling when atomic on PREEMPT_RT K Prateek Nayak
@ 2026-01-16 6:32 ` K Prateek Nayak
2026-01-16 6:32 ` [PATCH v3 2/2] cpufreq: Pass the policy to cpufreq_driver->adjust_perf() K Prateek Nayak
1 sibling, 0 replies; 3+ messages in thread
From: K Prateek Nayak @ 2026-01-16 6:32 UTC (permalink / raw)
To: Huang Rui, Gautham R. Shenoy, Mario Limonciello,
Rafael J. Wysocki, Viresh Kumar, Srinivas Pandruvada, Len Brown,
Sebastian Andrzej Siewior, Clark Williams, Bert Karwatzki,
linux-pm, linux-kernel, linux-rt-devel, rust-for-linux
Cc: Perry Yuan, K Prateek Nayak
All callers of amd_pstate_update() already have a reference to the
cpufreq_policy object.
Pass the entire policy object and grab the cpudata using
"policy->driver_data" instead of passing the cpudata and unnecessarily
grabbing another read-side reference to the cpufreq policy object when
it is already available in the caller.
No functional changes intended.
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
drivers/cpufreq/amd-pstate.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index c45bc98721d2..5818a92d96b9 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -565,15 +565,12 @@ static inline bool amd_pstate_sample(struct amd_cpudata *cpudata)
return true;
}
-static void amd_pstate_update(struct amd_cpudata *cpudata, u8 min_perf,
+static void amd_pstate_update(struct cpufreq_policy *policy, u8 min_perf,
u8 des_perf, u8 max_perf, bool fast_switch, int gov_flags)
{
- struct cpufreq_policy *policy __free(put_cpufreq_policy) = cpufreq_cpu_get(cpudata->cpu);
+ struct amd_cpudata *cpudata = policy->driver_data;
union perf_cached perf = READ_ONCE(cpudata->perf);
- if (!policy)
- return;
-
/* limit the max perf when core performance boost feature is disabled */
if (!cpudata->boost_supported)
max_perf = min_t(u8, perf.nominal_perf, max_perf);
@@ -675,7 +672,7 @@ static int amd_pstate_update_freq(struct cpufreq_policy *policy,
if (!fast_switch)
cpufreq_freq_transition_begin(policy, &freqs);
- amd_pstate_update(cpudata, perf.min_limit_perf, des_perf,
+ amd_pstate_update(policy, perf.min_limit_perf, des_perf,
perf.max_limit_perf, fast_switch,
policy->governor->flags);
@@ -737,7 +734,7 @@ static void amd_pstate_adjust_perf(unsigned int cpu,
if (max_perf < min_perf)
max_perf = min_perf;
- amd_pstate_update(cpudata, min_perf, des_perf, max_perf, true,
+ amd_pstate_update(policy, min_perf, des_perf, max_perf, true,
policy->governor->flags);
}
--
2.34.1
^ permalink raw reply [flat|nested] 3+ messages in thread* [PATCH v3 2/2] cpufreq: Pass the policy to cpufreq_driver->adjust_perf()
2026-01-16 6:32 [PATCH v3 0/2] cpufreq/amd-pstate: Prevent scheduling when atomic on PREEMPT_RT K Prateek Nayak
2026-01-16 6:32 ` [PATCH v3 1/2] cpufreq/amd-pstate: Pass the policy to amd_pstate_update() K Prateek Nayak
@ 2026-01-16 6:32 ` K Prateek Nayak
1 sibling, 0 replies; 3+ messages in thread
From: K Prateek Nayak @ 2026-01-16 6:32 UTC (permalink / raw)
To: Huang Rui, Gautham R. Shenoy, Mario Limonciello,
Rafael J. Wysocki, Viresh Kumar, Srinivas Pandruvada, Len Brown,
Sebastian Andrzej Siewior, Clark Williams, Bert Karwatzki,
linux-pm, linux-kernel, linux-rt-devel, rust-for-linux,
Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
Miguel Ojeda
Cc: Perry Yuan, K Prateek Nayak, Dietmar Eggemann, Steven Rostedt,
Ben Segall, Mel Gorman, Valentin Schneider, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich
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 v2..v3:
o Fixed the rust bindings for adjust_perf_callaback (kernel test robot).
---
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 +++--
rust/kernel/cpufreq.rs | 13 ++++++-------
6 files changed, 17 insertions(+), 18 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 object 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)
diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
index f968fbd22890..bea109f8ff78 100644
--- a/rust/kernel/cpufreq.rs
+++ b/rust/kernel/cpufreq.rs
@@ -1255,18 +1255,17 @@ impl<T: Driver> Registration<T> {
/// # Safety
///
/// - This function may only be called from the cpufreq C infrastructure.
+ /// - The pointer arguments must be valid pointers.
unsafe extern "C" fn adjust_perf_callback(
- cpu: c_uint,
+ ptr: *mut bindings::cpufreq_policy,
min_perf: c_ulong,
target_perf: c_ulong,
capacity: c_ulong,
) {
- // SAFETY: The C API guarantees that `cpu` refers to a valid CPU number.
- let cpu_id = unsafe { CpuId::from_u32_unchecked(cpu) };
-
- if let Ok(mut policy) = PolicyCpu::from_cpu(cpu_id) {
- T::adjust_perf(&mut policy, min_perf, target_perf, capacity);
- }
+ // SAFETY: The `ptr` is guaranteed to be valid by the contract with the C code for the
+ // lifetime of `policy`.
+ let policy = unsafe { Policy::from_raw_mut(ptr) };
+ T::adjust_perf(policy, min_perf, target_perf, capacity);
}
/// Driver's `get_intermediate` callback.
--
2.34.1
^ permalink raw reply [flat|nested] 3+ messages in thread