intel-idle: Fix CPU hotplug callback registration
authorSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Mon, 10 Mar 2014 20:40:30 +0000 (02:10 +0530)
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>
Thu, 20 Mar 2014 12:43:46 +0000 (13:43 +0100)
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>
drivers/idle/intel_idle.c

index 8e1939f564f4ae16f44d1f1b06e80744d303fa0b..51493ed4643b019a1cd80e423485a75f363b8dbe 100644 (file)
@@ -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;
 }