linux-kernel - [PATCH] ACPI: Fix initial QoS constraint application order in PPC initialization

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Message-ID: <20250718020312.856168-1-lijiayi@kylinos.cn>
Date: Fri, 18 Jul 2025 10:03:12 +0800
From: Jiayi Li <lijiayi@...inos.cn>
To: rafael@...nel.org,
	lenb@...nel.org
Cc: linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	jiayi_dec@....com,
	Jiayi Li <lijiayi@...inos.cn>
Subject: [PATCH] ACPI: Fix initial QoS constraint application order in PPC initialization

The original initialization sequence was:

cpufreq_policy_online()
    acpi_cpufreq_cpu_init()
        acpi_processor_get_platform_limit()
            freq_qos_update_request(&perflib_req)
    blocking_notifier_call_chain(...)
        acpi_processor_ppc_init()
            freq_qos_add_request(&perflib_req)

This caused a race condition where the QoS request was added after the
initial platform limit update. The new sequence explicitly ensures:

cpufreq_policy_online()
    acpi_cpufreq_cpu_init()
        acpi_processor_get_platform_limit()
            freq_qos_update_request(&perflib_req)
    blocking_notifier_call_chain(...)
        acpi_processor_ppc_init()
            freq_qos_add_request(&perflib_req)
+           acpi_processor_get_platform_limit()
+               freq_qos_update_request(&perflib_req)

The critical change adds an immediate platform limit update after the
QoS request is registered. This guarantees that the initial P-state
constraint is applied before any subsequent updates, resolving the window
where constraints could be applied out-of-order.

Fixes: d15ce412737a ("ACPI: cpufreq: Switch to QoS requests instead of cpufreq notifier")
Signed-off-by: Jiayi Li <lijiayi@...inos.cn>
---
 drivers/acpi/processor_perflib.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c
index 64b8d1e19594..3e7fe95c21d1 100644
--- a/drivers/acpi/processor_perflib.c
+++ b/drivers/acpi/processor_perflib.c
@@ -173,6 +173,9 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
 {
 	unsigned int cpu;
 
+	if (ignore_ppc == 1)
+		return;
+
 	for_each_cpu(cpu, policy->related_cpus) {
 		struct acpi_processor *pr = per_cpu(processors, cpu);
 		int ret;
@@ -193,6 +196,11 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
 		if (ret < 0)
 			pr_err("Failed to add freq constraint for CPU%d (%d)\n",
 			       cpu, ret);
+
+		ret = acpi_processor_get_platform_limit(pr);
+		if (ret)
+			pr_err("Failed to update freq constraint for CPU%d (%d)\n",
+			       cpu, ret);
 	}
 }
 
-- 
2.47.1