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Commit 3289705f authored by Srivatsa S. Bhat's avatar Srivatsa S. Bhat Committed by Rafael J. Wysocki
Browse files

hwmon, coretemp: Fix CPU hotplug callback registration 



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_notifier_register_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_notifier_register_done();

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

Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Jean Delvare <jdelvare@suse.de>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent cf0485a2

drivers/hwmon/coretemp.c

+7 −7
Original line number Diff line number Diff line
@@ -849,20 +849,20 @@ static int __init coretemp_init(void) 
	if (err)

		goto exit;



	get_online_cpus();

	cpu_notifier_register_begin();

	for_each_online_cpu(i)

		get_core_online(i);



#ifndef CONFIG_HOTPLUG_CPU

	if (list_empty(&pdev_list)) {

		put_online_cpus();

		cpu_notifier_register_done();

		err = -ENODEV;

		goto exit_driver_unreg;

	}

#endif



	register_hotcpu_notifier(&coretemp_cpu_notifier);

	put_online_cpus();

	__register_hotcpu_notifier(&coretemp_cpu_notifier);

	cpu_notifier_register_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_notifier_register_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_notifier_register_done();

	platform_driver_unregister(&coretemp_driver);

}