ia64, topology: 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 topology code in ia64 by using this latter form of callback
registration.

Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
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/arch/ia64/kernel/topology.c b/arch/ia64/kernel/topology.c
index ca69a5a96dcc07bb760eabd43ff6a03dfc2d6db2..f295f9abba4b04772679a6ff232a2f1387572c27 100644 (file)
--- a/arch/ia64/kernel/topology.c
+++ b/arch/ia64/kernel/topology.c
@@ -454,12 +454,16 @@ static int __init cache_sysfs_init(void)
 {
        int i;
 
+       cpu_notifier_register_begin();
+
        for_each_online_cpu(i) {
                struct device *sys_dev = get_cpu_device((unsigned int)i);
                cache_add_dev(sys_dev);
        }
 
-       register_hotcpu_notifier(&cache_cpu_notifier);
+       __register_hotcpu_notifier(&cache_cpu_notifier);
+
+       cpu_notifier_register_done();
 
        return 0;
 }