1 files changed, 18 insertions, 25 deletions

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index 7fc58af748b..bdea7e2f94b 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -64,21 +64,20 @@ struct cpu_dbs_info_s {
         unsigned int requested_freq;
         int cpu;
         unsigned int enable:1;
+        /*
+         * percpu mutex that serializes governor limit change with
+         * do_dbs_timer invocation. We do not want do_dbs_timer to run
+         * when user is changing the governor or limits.
+         */
+        struct mutex timer_mutex;
 };
 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
- * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, because it
- * would deadlock with cancel_delayed_work_sync(), which is needed for proper
- * raceless workqueue teardown.
+ * dbs_mutex protects data in dbs_tuners_ins from concurrent changes on
+ * different CPUs. It protects dbs_enable in governor start/stop.
  */
 static DEFINE_MUTEX(dbs_mutex);
 
@@ -488,18 +487,12 @@ static void do_dbs_timer(struct work_struct *work)
 
         delay -= jiffies % delay;
 
-        if (lock_policy_rwsem_write(cpu) < 0)
-                return;
-
-        if (!dbs_info->enable) {
-                unlock_policy_rwsem_write(cpu);
-                return;
-        }
+        mutex_lock(&dbs_info->timer_mutex);
 
         dbs_check_cpu(dbs_info);
 
         queue_delayed_work_on(cpu, kconservative_wq, &dbs_info->work, delay);
-        unlock_policy_rwsem_write(cpu);
+        mutex_unlock(&dbs_info->timer_mutex);
 }
 
 static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
@@ -535,9 +528,6 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                 if ((!cpu_online(cpu)) || (!policy->cur))
                         return -EINVAL;
 
-                if (this_dbs_info->enable) /* Already enabled */
-                        break;
-
                 mutex_lock(&dbs_mutex);
 
                 rc = sysfs_create_group(&policy->kobj, &dbs_attr_group);
@@ -561,6 +551,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                 this_dbs_info->down_skip = 0;
                 this_dbs_info->requested_freq = policy->cur;
 
+                mutex_init(&this_dbs_info->timer_mutex);
                 dbs_enable++;
                 /*
                  * Start the timerschedule work, when this governor
@@ -590,17 +581,19 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                                         &dbs_cpufreq_notifier_block,
                                         CPUFREQ_TRANSITION_NOTIFIER);
                 }
-                dbs_timer_init(this_dbs_info);
-
                 mutex_unlock(&dbs_mutex);
 
+                dbs_timer_init(this_dbs_info);
+
                 break;
 
         case CPUFREQ_GOV_STOP:
-                mutex_lock(&dbs_mutex);
                 dbs_timer_exit(this_dbs_info);
+
+                mutex_lock(&dbs_mutex);
                 sysfs_remove_group(&policy->kobj, &dbs_attr_group);
                 dbs_enable--;
+                mutex_destroy(&this_dbs_info->timer_mutex);
 
                 /*
                  * Stop the timerschedule work, when this governor
@@ -616,7 +609,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                 break;
 
         case CPUFREQ_GOV_LIMITS:
-                mutex_lock(&dbs_mutex);
+                mutex_lock(&this_dbs_info->timer_mutex);
                 if (policy->max < this_dbs_info->cur_policy->cur)
                         __cpufreq_driver_target(
                                         this_dbs_info->cur_policy,
@@ -625,7 +618,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                         __cpufreq_driver_target(
                                         this_dbs_info->cur_policy,
                                         policy->min, CPUFREQ_RELATION_L);
-                mutex_unlock(&dbs_mutex);
+                mutex_unlock(&this_dbs_info->timer_mutex);
 
                 break;
         }