[PATCH] Reorganize the cpufreq cpu hotplug locking to not be totally bizare

The patch below moves the cpu hotplugging higher up in the cpufreq
layering; this is needed to avoid recursive taking of the cpu hotplug
lock and to otherwise detangle the mess.

The new rules are:
1. you must do lock_cpu_hotplug() around the following functions:
   __cpufreq_driver_target
   __cpufreq_governor (for CPUFREQ_GOV_LIMITS operation only)
   __cpufreq_set_policy
2. governer methods (.governer) must NOT take the lock_cpu_hotplug()
   lock in any way; they are called with the lock taken already
3. if your governer spawns a thread that does things, like calling
   __cpufreq_driver_target, your thread must honor rule #1.
4. the policy lock and other cpufreq internal locks nest within
   the lock_cpu_hotplug() lock.

I'm not entirely happy about how the __cpufreq_governor rule ended up
(conditional locking rule depending on the argument) but basically all
callers pass this as a constant so it's not too horrible.

The patch also removes the cpufreq_governor() function since during the
locking audit it turned out to be entirely unused (so no need to fix it)

The patch works on my testbox, but it could use more testing
(otoh... it can't be much worse than the current code)

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 18 insertions, 22 deletions

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 8d328186f774..bc1088d9b379 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -364,10 +364,12 @@ static ssize_t store_##file_name					\
         if (ret != 1)                                                   \
                 return -EINVAL;                                         \
                                                                         \
+        lock_cpu_hotplug();                                             \
         mutex_lock(&policy->lock);                                      \
         ret = __cpufreq_set_policy(policy, &new_policy);                \
         policy->user_policy.object = policy->object;                    \
         mutex_unlock(&policy->lock);                                    \
+        unlock_cpu_hotplug();                                           \
                                                                         \
         return ret ? ret : count;                                       \
 }
@@ -1197,20 +1199,18 @@ EXPORT_SYMBOL(cpufreq_unregister_notifier);
  *********************************************************************/
 
 
+/* Must be called with lock_cpu_hotplug held */
 int __cpufreq_driver_target(struct cpufreq_policy *policy,
                             unsigned int target_freq,
                             unsigned int relation)
 {
         int retval = -EINVAL;
 
-        lock_cpu_hotplug();
         dprintk("target for CPU %u: %u kHz, relation %u\n", policy->cpu,
                 target_freq, relation);
         if (cpu_online(policy->cpu) && cpufreq_driver->target)
                 retval = cpufreq_driver->target(policy, target_freq, relation);
 
-        unlock_cpu_hotplug();
-
         return retval;
 }
 EXPORT_SYMBOL_GPL(__cpufreq_driver_target);
@@ -1225,17 +1225,23 @@ int cpufreq_driver_target(struct cpufreq_policy *policy,
         if (!policy)
                 return -EINVAL;
 
+        lock_cpu_hotplug();
         mutex_lock(&policy->lock);
 
         ret = __cpufreq_driver_target(policy, target_freq, relation);
 
         mutex_unlock(&policy->lock);
+        unlock_cpu_hotplug();
 
         cpufreq_cpu_put(policy);
         return ret;
 }
 EXPORT_SYMBOL_GPL(cpufreq_driver_target);
 
+/*
+ * Locking: Must be called with the lock_cpu_hotplug() lock held
+ * when "event" is CPUFREQ_GOV_LIMITS
+ */
 
 static int __cpufreq_governor(struct cpufreq_policy *policy, unsigned int event)
 {
@@ -1257,24 +1263,6 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, unsigned int event)
 }
 
 
-int cpufreq_governor(unsigned int cpu, unsigned int event)
-{
-        int ret = 0;
-        struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
-
-        if (!policy)
-                return -EINVAL;
-
-        mutex_lock(&policy->lock);
-        ret = __cpufreq_governor(policy, event);
-        mutex_unlock(&policy->lock);
-
-        cpufreq_cpu_put(policy);
-        return ret;
-}
-EXPORT_SYMBOL_GPL(cpufreq_governor);
-
-
 int cpufreq_register_governor(struct cpufreq_governor *governor)
 {
         struct cpufreq_governor *t;
@@ -1342,6 +1330,9 @@ int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu)
 EXPORT_SYMBOL(cpufreq_get_policy);
 
 
+/*
+ * Locking: Must be called with the lock_cpu_hotplug() lock held
+ */
 static int __cpufreq_set_policy(struct cpufreq_policy *data, struct cpufreq_policy *policy)
 {
         int ret = 0;
@@ -1436,6 +1427,8 @@ int cpufreq_set_policy(struct cpufreq_policy *policy)
         if (!data)
                 return -EINVAL;
 
+        lock_cpu_hotplug();
+
         /* lock this CPU */
         mutex_lock(&data->lock);
 
@@ -1446,6 +1439,8 @@ int cpufreq_set_policy(struct cpufreq_policy *policy)
         data->user_policy.governor = data->governor;
 
         mutex_unlock(&data->lock);
+
+        unlock_cpu_hotplug();
         cpufreq_cpu_put(data);
 
         return ret;
@@ -1469,6 +1464,7 @@ int cpufreq_update_policy(unsigned int cpu)
         if (!data)
                 return -ENODEV;
 
+        lock_cpu_hotplug();
         mutex_lock(&data->lock);
 
         dprintk("updating policy for CPU %u\n", cpu);
@@ -1494,7 +1490,7 @@ int cpufreq_update_policy(unsigned int cpu)
         ret = __cpufreq_set_policy(data, &policy);
 
         mutex_unlock(&data->lock);
-
+        unlock_cpu_hotplug();
         cpufreq_cpu_put(data);
         return ret;
 }