Commit c0379108 authored by K Prateek Nayak's avatar K Prateek Nayak Committed by Mario Limonciello (AMD)
Browse files

cpufreq: Pass the policy to cpufreq_driver->adjust_perf() 

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.

Closes:https://lore.kernel.org/all/20250731092316.3191-1-spasswolf@web.de/

 [1]

Fixes: 1d215f03 ("cpufreq: amd-pstate: Add fast switch function for AMD P-State")
Reported-by: default avatarBert Karwatzki <spasswolf@web.de>
Acked-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: default avatarK Prateek Nayak <kprateek.nayak@amd.com>
Acked-by: Gary Guo <gary@garyguo.net> # Rust
Reviewed-by: default avatarGautham R. Shenoy <gautham.shenoy@amd.com>
Reviewed-by: default avatarZhongqiu Han <zhongqiu.han@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260316081849.19368-3-kprateek.nayak@amd.com


Signed-off-by: default avatarMario Limonciello (AMD) <superm1@kernel.org>
parent 86d71f1d

drivers/cpufreq/amd-pstate.c

+1 −2
Original line number Diff line number Diff line
@@ -788,13 +788,12 @@ 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;

drivers/cpufreq/cpufreq.c

+3 −3
Original line number Diff line number Diff line
@@ -2231,7 +2231,7 @@ 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.
@@ -2250,12 +2250,12 @@ 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);

}



/**

drivers/cpufreq/intel_pstate.c

+2 −2
Original line number Diff line number Diff line
@@ -3239,12 +3239,12 @@ 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;

include/linux/cpufreq.h

+2 −2
Original line number Diff line number Diff line
@@ -372,7 +372,7 @@ 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);
@@ -617,7 +617,7 @@ 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);

kernel/sched/cpufreq_schedutil.c

+3 −2
Original line number Diff line number Diff line
@@ -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)