From: Doug Chapman <dchapman@redhat.com>
Date: Thu, 6 Dec 2007 16:15:55 -0500
Subject: [cpufreq] remove hotplug cpu cruft
Message-id: 1196975755.1083.9.camel@athlon
O-Subject: [RHEL 5.2 PATCH 4/5] hang at 'Disabling ondemand cpu frequency scaling'
Bugzilla: 253416

Patch 4/5 for BZ 253416

It was recommended by Dave Jones that I include this patch.

Backport of:

commit c120069779e3e35917c15393cf2847fa79811eb6
Author: Dave Jones <davej@redhat.com>
Date:   Mon Feb 5 16:12:43 2007 -0800

    [CPUFREQ] Remove hotplug cpu crap

    The hotplug CPU locking in cpufreq is horrendous.  No-one seems to care
    enough to fix it, so just remove it so that the 99.9% of the real world
    users of this code can use cpufreq without being bothered by warnings.

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 66b274d..5ee1b94 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -453,10 +453,8 @@ static ssize_t store_##file_name					\
 	if (ret != 1)							\
 		return -EINVAL;						\
 									\
-	lock_cpu_hotplug();						\
 	ret = __cpufreq_set_policy(policy, &new_policy);		\
 	policy->user_policy.object = policy->object;			\
-	unlock_cpu_hotplug();						\
 									\
 	return ret ? ret : count;					\
 }
@@ -512,8 +510,6 @@ static ssize_t store_scaling_governor (struct cpufreq_policy * policy,
 	if (cpufreq_parse_governor(str_governor, &new_policy.policy, &new_policy.governor))
 		return -EINVAL;
 
-	lock_cpu_hotplug();
-
 	/* Do not use cpufreq_set_policy here or the user_policy.max
 	   will be wrongly overridden */
 	ret = __cpufreq_set_policy(policy, &new_policy);
@@ -521,8 +517,6 @@ static ssize_t store_scaling_governor (struct cpufreq_policy * policy,
 	policy->user_policy.policy = policy->policy;
 	policy->user_policy.governor = policy->governor;
 
-	unlock_cpu_hotplug();
-
 	return ret ? ret : count;
 }
 
@@ -1342,7 +1336,6 @@ 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)
@@ -1368,14 +1361,12 @@ int cpufreq_driver_target(struct cpufreq_policy *policy,
 	if (!policy)
 		return -EINVAL;
 
-	lock_cpu_hotplug();
 	if (unlikely(lock_policy_rwsem_write(policy->cpu)))
 		return -EINVAL;
 
 	ret = __cpufreq_driver_target(policy, target_freq, relation);
 
 	unlock_policy_rwsem_write(policy->cpu);
-	unlock_cpu_hotplug();
 
 	cpufreq_cpu_put(policy);
 	return ret;
@@ -1383,7 +1374,6 @@ int cpufreq_driver_target(struct cpufreq_policy *policy,
 EXPORT_SYMBOL_GPL(cpufreq_driver_target);
 
 /*
- * Locking: Must be called with the lock_cpu_hotplug() lock held
  * when "event" is CPUFREQ_GOV_LIMITS
  */
 
@@ -1470,9 +1460,6 @@ 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;
@@ -1572,8 +1559,6 @@ int cpufreq_set_policy(struct cpufreq_policy *policy)
 	if (!data)
 		return -EINVAL;
 
-	lock_cpu_hotplug();
-
 	if (unlikely(lock_policy_rwsem_write(policy->cpu)))
 		return -EINVAL;
 
@@ -1586,7 +1571,6 @@ int cpufreq_set_policy(struct cpufreq_policy *policy)
 
 	unlock_policy_rwsem_write(policy->cpu);
 
-	unlock_cpu_hotplug();
 	cpufreq_cpu_put(data);
 
 	return ret;
@@ -1610,7 +1594,6 @@ int cpufreq_update_policy(unsigned int cpu)
 	if (!data)
 		return -ENODEV;
 
-	lock_cpu_hotplug();
 	if (unlikely(lock_policy_rwsem_write(cpu)))
 		return -EINVAL;
 
@@ -1638,7 +1621,6 @@ int cpufreq_update_policy(unsigned int cpu)
 
 	unlock_policy_rwsem_write(cpu);
 
-	unlock_cpu_hotplug();
 	cpufreq_cpu_put(data);
 	return ret;
 }
diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index c4c578d..4a5f921 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -73,14 +73,6 @@ static DEFINE_PER_CPU(struct cpu_dbs_info_s, cpu_dbs_info);
 
 static unsigned int dbs_enable;	/* number of CPUs using this policy */
 
-/*
- * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug
- * lock and dbs_mutex. cpu_hotplug lock should always be held before
- * dbs_mutex. If any function that can potentially take cpu_hotplug lock
- * (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then
- * cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock
- * is recursive for the same process. -Venki
- */
 static DEFINE_MUTEX 	(dbs_mutex);
 static DECLARE_WORK	(dbs_work, do_dbs_timer, NULL);
 
@@ -423,14 +415,12 @@ static void dbs_check_cpu(int cpu)
 static void do_dbs_timer(void *data)
 { 
 	int i;
-	lock_cpu_hotplug();
 	mutex_lock(&dbs_mutex);
 	for_each_online_cpu(i)
 		dbs_check_cpu(i);
 	schedule_delayed_work(&dbs_work, 
 			usecs_to_jiffies(dbs_tuners_ins.sampling_rate));
 	mutex_unlock(&dbs_mutex);
-	unlock_cpu_hotplug();
 } 
 
 static inline void dbs_timer_init(void)
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 9218115..9853ef5 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -315,9 +315,7 @@ static void do_dbs_timer(struct cpu_dbs_info_s *dbs_info)
 		return;
 	}
 
-	lock_cpu_hotplug();
 	dbs_check_cpu(dbs_info);
-	unlock_cpu_hotplug();
 	queue_delayed_work_on(cpu, kondemand_wq, &dbs_info->work,
 			usecs_to_jiffies(dbs_tuners_ins.sampling_rate));
 	unlock_policy_rwsem_write(cpu);
diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
index c2ecc59..9926997 100644
--- a/drivers/cpufreq/cpufreq_stats.c
+++ b/drivers/cpufreq/cpufreq_stats.c
@@ -366,12 +366,10 @@ __exit cpufreq_stats_exit(void)
 	cpufreq_unregister_notifier(&notifier_trans_block,
 			CPUFREQ_TRANSITION_NOTIFIER);
 	unregister_hotcpu_notifier(&cpufreq_stat_cpu_notifier);
-	lock_cpu_hotplug();
 	for_each_online_cpu(cpu) {
 		cpufreq_stat_cpu_callback(&cpufreq_stat_cpu_notifier, CPU_DEAD,
 			(void *)(long)cpu);
 	}
-	unlock_cpu_hotplug();
 }
 
 MODULE_AUTHOR ("Zou Nan hai <nanhai.zou@intel.com>");
diff --git a/drivers/cpufreq/cpufreq_userspace.c b/drivers/cpufreq/cpufreq_userspace.c
index a06c204..29ada96 100644
--- a/drivers/cpufreq/cpufreq_userspace.c
+++ b/drivers/cpufreq/cpufreq_userspace.c
@@ -71,7 +71,6 @@ static int cpufreq_set(unsigned int freq, struct cpufreq_policy *policy)
 
 	dprintk("cpufreq_set for cpu %u, freq %u kHz\n", policy->cpu, freq);
 
-	lock_cpu_hotplug();
 	mutex_lock(&userspace_mutex);
 	if (!cpu_is_managed[policy->cpu])
 		goto err;
@@ -94,7 +93,6 @@ static int cpufreq_set(unsigned int freq, struct cpufreq_policy *policy)
 
  err:
 	mutex_unlock(&userspace_mutex);
-	unlock_cpu_hotplug();
 	return ret;
 }