- cpufreq-ondemand-vs-suspend-deadlock-fix.patch removed from -mm tree

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The patch titled

     cpufreq: ondemand vs suspend deadlock fix

has been removed from the -mm tree.  Its filename is

     cpufreq-ondemand-vs-suspend-deadlock-fix.patch

This patch was dropped because it was merged into mainline or a subsystem tree

------------------------------------------------------
Subject: cpufreq: ondemand vs suspend deadlock fix
From: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>


Root caused this to a deadlock in cpufreq and ondemand.  The deadlock is
due to non-existant ordering between cpu_hotplug lock and dbs_mutex. 
Basically a race condition between cpu_down() and do_dbs_timer().

cpu_down() flow:
1 cpu_down() for CPU 1
2 Takes the cpu_hotplug lock
3 Calls pre-down notifiers
4   notifier handler in cpufreq calls cpufreq_driver_target
5     cpufreq_driver_target calls cpu_hotplu lock/unlock
      It is OK as cpu_hotplug lock is recusive for same process
6 CPU 1 goes down
7 CPU 0 calls post down notifiers for CPU 1
8   notifier handler in cpufreq calls governor event for stop
9     this ondemand governor routine takes dbs_mutex

Basically cpu_hotplug lock being taken before dbs_mutex in this path.

There is another event that gets triggered periodically in do_dbs_timer(). 
This runs in the context of ondemand workqueue and it takes dbs_mutex first
and takes cpu_hotplug later, inside __cpufreq_driver_target() call.  This
ordering conflicts with mutex ordering in cpu_down and causes a deadlock.

Attached patch fixes the issue for both ondemand and conservative governors.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

 drivers/cpufreq/cpufreq_conservative.c |   12 ++++++++++++
 drivers/cpufreq/cpufreq_ondemand.c     |   12 ++++++++++++
 2 files changed, 24 insertions(+)

diff -puN drivers/cpufreq/cpufreq_conservative.c~cpufreq-ondemand-vs-suspend-deadlock-fix drivers/cpufreq/cpufreq_conservative.c
--- a/drivers/cpufreq/cpufreq_conservative.c~cpufreq-ondemand-vs-suspend-deadlock-fix
+++ a/drivers/cpufreq/cpufreq_conservative.c
@@ -72,6 +72,14 @@ static DEFINE_PER_CPU(struct cpu_dbs_inf
 
 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);
 
@@ -414,12 +422,14 @@ 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)
@@ -514,6 +524,7 @@ static int cpufreq_governor_dbs(struct c
 		break;
 
 	case CPUFREQ_GOV_LIMITS:
+		lock_cpu_hotplug();
 		mutex_lock(&dbs_mutex);
 		if (policy->max < this_dbs_info->cur_policy->cur)
 			__cpufreq_driver_target(
@@ -524,6 +535,7 @@ static int cpufreq_governor_dbs(struct c
 					this_dbs_info->cur_policy,
 				       	policy->min, CPUFREQ_RELATION_L);
 		mutex_unlock(&dbs_mutex);
+		unlock_cpu_hotplug();
 		break;
 	}
 	return 0;
diff -puN drivers/cpufreq/cpufreq_ondemand.c~cpufreq-ondemand-vs-suspend-deadlock-fix drivers/cpufreq/cpufreq_ondemand.c
--- a/drivers/cpufreq/cpufreq_ondemand.c~cpufreq-ondemand-vs-suspend-deadlock-fix
+++ a/drivers/cpufreq/cpufreq_ondemand.c
@@ -71,6 +71,14 @@ static DEFINE_PER_CPU(struct cpu_dbs_inf
 
 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);
 
@@ -363,12 +371,14 @@ 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);
 	queue_delayed_work(dbs_workq, &dbs_work,
 			   usecs_to_jiffies(dbs_tuners_ins.sampling_rate));
 	mutex_unlock(&dbs_mutex);
+	unlock_cpu_hotplug();
 }
 
 static inline void dbs_timer_init(void)
@@ -469,6 +479,7 @@ static int cpufreq_governor_dbs(struct c
 		break;
 
 	case CPUFREQ_GOV_LIMITS:
+		lock_cpu_hotplug();
 		mutex_lock(&dbs_mutex);
 		if (policy->max < this_dbs_info->cur_policy->cur)
 			__cpufreq_driver_target(
@@ -479,6 +490,7 @@ static int cpufreq_governor_dbs(struct c
 					this_dbs_info->cur_policy,
 					policy->min, CPUFREQ_RELATION_L);
 		mutex_unlock(&dbs_mutex);
+		unlock_cpu_hotplug();
 		break;
 	}
 	return 0;
_

Patches currently in -mm which might be from venkatesh.pallipadi@xxxxxxxxx are

git-acpi.patch
git-cpufreq.patch
hpet-rtc-emulation-add-watchdog-timer.patch

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