linux-kernel - [PATCH v1 1/6] thermal: cpu_cooling: Fix the notification mechanism by using per cpu structure

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Date:	Thu, 29 May 2014 13:45:29 +0530
From:	Amit Daniel Kachhap <amit.daniel@...sung.com>
To:	linux-pm@...r.kernel.org, linux-acpi@...r.kernel.org
Cc:	Zhang Rui <rui.zhang@...el.com>, linux-kernel@...r.kernel.org,
	amit.kachhap@...il.com, edubezval@...il.com, rjw@...ysocki.net,
	linux-arm-kernel@...ts.infradead.org, lenb@...nel.org
Subject: [PATCH v1 1/6] thermal: cpu_cooling: Fix the notification mechanism by using per cpu structure

Currently the notification data is supplied to the thermal notifiers using
a single global pointer. This method will have race condition if cpu cooling
interfaces are used by more than 1 clients (more than 1 cdev) to cause cpufreq
clipping. Also the notifier data is presented as per cpu cpufreq policy
structure. This was needed as same cpu is used later in thermal cpufreq handler
function.

Signed-off-by: Amit Daniel Kachhap <amit.daniel@...sung.com>
---
 drivers/thermal/cpu_cooling.c |   38 +++++++++++++++-----------------------
 1 files changed, 15 insertions(+), 23 deletions(-)

diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
index 4246262..16388b0 100644
--- a/drivers/thermal/cpu_cooling.c
+++ b/drivers/thermal/cpu_cooling.c
@@ -58,7 +58,7 @@ static unsigned int cpufreq_dev_count;
 
 /* notify_table passes value to the CPUFREQ_ADJUST callback function. */
 #define NOTIFY_INVALID NULL
-static struct cpufreq_cooling_device *notify_device;
+static DEFINE_PER_CPU(struct cpufreq_cooling_device *, notify_device);
 
 /**
  * get_idr - function to get a unique id.
@@ -98,23 +98,6 @@ static void release_idr(struct idr *idr, int id)
 
 /* Below code defines functions to be used for cpufreq as cooling device */
 
-/**
- * is_cpufreq_valid - function to check frequency transitioning capability.
- * @cpu: cpu for which check is needed.
- *
- * This function will check the current state of the system if
- * it is capable of changing the frequency for a given @cpu.
- *
- * Return: 0 if the system is not currently capable of changing
- * the frequency of given cpu. !0 in case the frequency is changeable.
- */
-static int is_cpufreq_valid(int cpu)
-{
-	struct cpufreq_policy policy;
-
-	return !cpufreq_get_policy(&policy, cpu);
-}
-
 enum cpufreq_cooling_property {
 	GET_LEVEL,
 	GET_FREQ,
@@ -294,11 +277,18 @@ static int cpufreq_apply_cooling(struct cpufreq_cooling_device *cpufreq_device,
 
 	cpufreq_device->cpufreq_state = cooling_state;
 	cpufreq_device->cpufreq_val = clip_freq;
-	notify_device = cpufreq_device;
 
 	for_each_cpu(cpuid, mask) {
-		if (is_cpufreq_valid(cpuid))
+		if (cpufreq_get_policy(&policy, cpu) == 0) {
+			/*
+			 * Store the notification data in the cpu pointed by
+			 * cpufreq policy structure. This is needed as this cpu
+			 * will be used later to fetch correct data pointer.
+			 */
+			per_cpu(notify_device, policy.cpu) = cpufreq_device;
 			cpufreq_update_policy(cpuid);
+			per_cpu(notify_device, policy.cpu) = NOTIFY_INVALID;
+		}
 	}
 
 	notify_device = NOTIFY_INVALID;
@@ -323,12 +313,14 @@ static int cpufreq_thermal_notifier(struct notifier_block *nb,
 {
 	struct cpufreq_policy *policy = data;
 	unsigned long max_freq = 0;
+	struct cpufreq_cooling_device *cpufreq_device
+				= per_cpu(notify_device, policy->cpu);
 
-	if (event != CPUFREQ_ADJUST || notify_device == NOTIFY_INVALID)
+	if (event != CPUFREQ_ADJUST || cpufreq_device == NOTIFY_INVALID)
 		return 0;
 
-	if (cpumask_test_cpu(policy->cpu, &notify_device->allowed_cpus))
-		max_freq = notify_device->cpufreq_val;
+	if (cpumask_test_cpu(policy->cpu, &cpufreq_device->allowed_cpus))
+		max_freq = cpufreq_device->cpufreq_val;
 	else
 		return 0;
 
-- 
1.7.1

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