[CPUFREQ] ondemand governor use new cpufreq rwsem locking in work callback

Eliminate flush_workqueue in cpufreq_governor(STOP) callpath. Using flush
there has a deadlock potential as in

http://uwsg.iu.edu/hypermail/linux/kernel/0611.3/1223.html

Also, cleanup the locking issues with do_dbs_timer delayed_work callback.  As
it changes the CPU frequency using __cpufreq_target, it needs to have
policy_rwsem in write mode, which also protects it from hot plug.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>

1 files changed, 16 insertions, 18 deletions

diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index a480834c9627..bcf8bb877a8b 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -437,8 +437,14 @@ static void do_dbs_timer(struct work_struct *work)
 
         delay -= jiffies % delay;
 
-        if (!dbs_info->enable)
+        if (lock_policy_rwsem_write(cpu) < 0)
                 return;
+
+        if (!dbs_info->enable) {
+                unlock_policy_rwsem_write(cpu);
+                return;
+        }
+
         /* Common NORMAL_SAMPLE setup */
         dbs_info->sample_type = DBS_NORMAL_SAMPLE;
         if (!dbs_tuners_ins.powersave_bias ||
@@ -455,6 +461,7 @@ static void do_dbs_timer(struct work_struct *work)
                                         CPUFREQ_RELATION_H);
         }
         queue_delayed_work_on(cpu, kondemand_wq, &dbs_info->work, delay);
+        unlock_policy_rwsem_write(cpu);
 }
 
 static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
@@ -463,6 +470,7 @@ static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
         int delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
         delay -= jiffies % delay;
 
+        dbs_info->enable = 1;
         ondemand_powersave_bias_init();
         dbs_info->sample_type = DBS_NORMAL_SAMPLE;
         INIT_DELAYED_WORK_NAR(&dbs_info->work, do_dbs_timer);
@@ -474,7 +482,6 @@ static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
 {
         dbs_info->enable = 0;
         cancel_delayed_work(&dbs_info->work);
-        flush_workqueue(kondemand_wq);
 }
 
 static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
@@ -503,21 +510,9 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 
                 mutex_lock(&dbs_mutex);
                 dbs_enable++;
-                if (dbs_enable == 1) {
-                        kondemand_wq = create_workqueue("kondemand");
-                        if (!kondemand_wq) {
-                                printk(KERN_ERR
-                                         "Creation of kondemand failed\n");
-                                dbs_enable--;
-                                mutex_unlock(&dbs_mutex);
-                                return -ENOSPC;
-                        }
-                }
 
                 rc = sysfs_create_group(&policy->kobj, &dbs_attr_group);
                 if (rc) {
-                        if (dbs_enable == 1)
-                                destroy_workqueue(kondemand_wq);
                         dbs_enable--;
                         mutex_unlock(&dbs_mutex);
                         return rc;
@@ -532,7 +527,6 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                         j_dbs_info->prev_cpu_wall = get_jiffies_64();
                 }
                 this_dbs_info->cpu = cpu;
-                this_dbs_info->enable = 1;
                 /*
                  * Start the timerschedule work, when this governor
                  * is used for first time
@@ -562,9 +556,6 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                 dbs_timer_exit(this_dbs_info);
                 sysfs_remove_group(&policy->kobj, &dbs_attr_group);
                 dbs_enable--;
-                if (dbs_enable == 0)
-                        destroy_workqueue(kondemand_wq);
-
                 mutex_unlock(&dbs_mutex);
 
                 break;
@@ -593,12 +584,18 @@ static struct cpufreq_governor cpufreq_gov_dbs = {
 
 static int __init cpufreq_gov_dbs_init(void)
 {
+        kondemand_wq = create_workqueue("kondemand");
+        if (!kondemand_wq) {
+                printk(KERN_ERR "Creation of kondemand failed\n");
+                return -EFAULT;
+        }
         return cpufreq_register_governor(&cpufreq_gov_dbs);
 }
 
 static void __exit cpufreq_gov_dbs_exit(void)
 {
         cpufreq_unregister_governor(&cpufreq_gov_dbs);
+        destroy_workqueue(kondemand_wq);
 }
 
 
@@ -610,3 +607,4 @@ MODULE_LICENSE("GPL");
 
 module_init(cpufreq_gov_dbs_init);
 module_exit(cpufreq_gov_dbs_exit);
+