[PATCH 42/51] hwmon, coretemp: Fix CPU hotplug callback registration

[Srivatsa S. Bhat]

Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_maps_update_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_maps_update_done();


Fix the hwmon coretemp code by using this latter form of callback
registration.

Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Jean Delvare <jdelvare@xxxxxxx>
Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: lm-sensors@xxxxxxxxxxxxxx
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

 drivers/hwmon/coretemp.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index bbb0b0d..43c436b 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -849,20 +849,20 @@ static int __init coretemp_init(void)
 	if (err)
 		goto exit;
 
-	get_online_cpus();
+	cpu_maps_update_begin();
 	for_each_online_cpu(i)
 		get_core_online(i);
 
 #ifndef CONFIG_HOTPLUG_CPU
 	if (list_empty(&pdev_list)) {
-		put_online_cpus();
+		cpu_maps_update_done();
 		err = -ENODEV;
 		goto exit_driver_unreg;
 	}
 #endif
 
-	register_hotcpu_notifier(&coretemp_cpu_notifier);
-	put_online_cpus();
+	__register_hotcpu_notifier(&coretemp_cpu_notifier);
+	cpu_maps_update_done();
 	return 0;
 
 #ifndef CONFIG_HOTPLUG_CPU
@@ -877,8 +877,8 @@ static void __exit coretemp_exit(void)
 {
 	struct pdev_entry *p, *n;
 
-	get_online_cpus();
-	unregister_hotcpu_notifier(&coretemp_cpu_notifier);
+	cpu_maps_update_begin();
+	__unregister_hotcpu_notifier(&coretemp_cpu_notifier);
 	mutex_lock(&pdev_list_mutex);
 	list_for_each_entry_safe(p, n, &pdev_list, list) {
 		platform_device_unregister(p->pdev);
@@ -886,7 +886,7 @@ static void __exit coretemp_exit(void)
 		kfree(p);
 	}
 	mutex_unlock(&pdev_list_mutex);
-	put_online_cpus();
+	cpu_maps_update_done();
 	platform_driver_unregister(&coretemp_driver);
 }
 

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