tree b4021a25d0da5fdebd2d87c81c5a0b1df10fb022
parent cf0485a2ac70acb1bc83f6310a7ebef3070f0333
author Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> 1394484071 +0530
committer Rafael J. Wysocki <rafael.j.wysocki@intel.com> 1395319427 +0100

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: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>