Merge "cpufreq: ondemand: Resolve deadlock when waking up dbs sync thread"

drivers/cpufreq/cpufreq_ondemand.c

@@ -4,7 +4,7 @@
  *  Copyright (C)  2001 Russell King
  *            (C)  2003 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>.
  *                      Jun Nakajima <jun.nakajima@intel.com>
- *            (c)  2013 The Linux Foundation. All rights reserved.
+ *            (c)  2013, 2015 The Linux Foundation. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -108,6 +108,7 @@ struct cpu_dbs_info_s {
 	struct task_struct *sync_thread;
 	wait_queue_head_t sync_wq;
 	atomic_t src_sync_cpu;
+	atomic_t being_woken;
 	atomic_t sync_enabled;
 };
 static DEFINE_PER_CPU(struct cpu_dbs_info_s, od_cpu_dbs_info);
@@ -1087,7 +1088,16 @@ static int dbs_migration_notify(struct notifier_block *nb,
 		&per_cpu(od_cpu_dbs_info, target_cpu);
 
 	atomic_set(&target_dbs_info->src_sync_cpu, (int)arg);
-	wake_up(&target_dbs_info->sync_wq);
+	/*
+	* Avoid issuing recursive wakeup call, as sync thread itself could be
+	* seen as migrating triggering this notification. Note that sync thread
+	* of a cpu could be running for a short while with its affinity broken
+	* because of CPU hotplug.
+	*/
+	if (!atomic_cmpxchg(&target_dbs_info->being_woken, 0, 1)) {
+		wake_up(&target_dbs_info->sync_wq);
+		atomic_set(&target_dbs_info->being_woken, 0);
+	}
 
 	return NOTIFY_OK;
 }
@@ -1442,6 +1452,7 @@ static int __init cpufreq_gov_dbs_init(void)
 		dbs_work->cpu = i;
 
 		atomic_set(&this_dbs_info->src_sync_cpu, -1);
+		atomic_set(&this_dbs_info->being_woken, 0);
 		init_waitqueue_head(&this_dbs_info->sync_wq);
 
 		this_dbs_info->sync_thread = kthread_run(dbs_sync_thread,