intel-idle: 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 intel-idle code by using this latter form of callback registration.

Cc: Len Brown <lenb@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 8e1939f564f4ae16f44d1f1b06e80744d303fa0b..51493ed4643b019a1cd80e423485a75f363b8dbe 100644 (file)
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -681,14 +681,19 @@ static int __init intel_idle_init(void)
        if (intel_idle_cpuidle_devices == NULL)
                return -ENOMEM;
 
+       cpu_notifier_register_begin();
+
        for_each_online_cpu(i) {
                retval = intel_idle_cpu_init(i);
                if (retval) {
+                       cpu_notifier_register_done();
                        cpuidle_unregister_driver(&intel_idle_driver);
                        return retval;
                }
        }
-       register_cpu_notifier(&cpu_hotplug_notifier);
+       __register_cpu_notifier(&cpu_hotplug_notifier);
+
+       cpu_notifier_register_done();
 
        return 0;
 }
@@ -698,10 +703,13 @@ static void __exit intel_idle_exit(void)
        intel_idle_cpuidle_devices_uninit();
        cpuidle_unregister_driver(&intel_idle_driver);
 
+       cpu_notifier_register_begin();
 
        if (lapic_timer_reliable_states != LAPIC_TIMER_ALWAYS_RELIABLE)
                on_each_cpu(__setup_broadcast_timer, (void *)false, 1);
-       unregister_cpu_notifier(&cpu_hotplug_notifier);
+       __unregister_cpu_notifier(&cpu_hotplug_notifier);
+
+       cpu_notifier_register_done();
 
        return;
 }