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

Amit Daniel Kachhap
2014-05-29T08:16:06Z

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@samsung.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