+ However, if you want to register a hotplug callback, as well as perform
+ some initialization for CPUs that are already online, then do this:
+
+ Version 1: (Correct)
+ ---------
+
+ cpu_notifier_register_begin();
+
+ for_each_online_cpu(i) {
+ foobar_cpu_callback(&foobar_cpu_notifier,
+ CPU_UP_PREPARE, i);
+ foobar_cpu_callback(&foobar_cpu_notifier,
+ CPU_ONLINE, i);
+ }
+
+ /* Note the use of the double underscored version of the API */
+ __register_cpu_notifier(&foobar_cpu_notifier);
+
+ cpu_notifier_register_done();
+
+ Note that the following code is *NOT* the right way to achieve this,
+ because it is prone to an ABBA deadlock between the cpu_add_remove_lock
+ and the cpu_hotplug.lock.
+
+ Version 2: (Wrong!)
+ ---------
+
+ get_online_cpus();
+
+ for_each_online_cpu(i) {
+ foobar_cpu_callback(&foobar_cpu_notifier,
+ CPU_UP_PREPARE, i);
+ foobar_cpu_callback(&foobar_cpu_notifier,
+ CPU_ONLINE, i);
+ }
+
+ register_cpu_notifier(&foobar_cpu_notifier);
+
+ put_online_cpus();
+
+ So always use the first version shown above when you want to register
+ callbacks as well as initialize the already online CPUs.
+
+