drivers/base/topology.c: 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 by using this latter form of callback registration.

Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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/base/topology.c b/drivers/base/topology.c
index 94ffee378f103d6cd2018497a5f1a93ebcde9baf..a738d1069d6bc0f353e19fbe79a2702f7848e3b7 100644 (file)
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -161,16 +161,20 @@ static int topology_cpu_callback(struct notifier_block *nfb,
 static int topology_sysfs_init(void)
 {
        int cpu;
-       int rc;
+       int rc = 0;
+
+       cpu_notifier_register_begin();
 
        for_each_online_cpu(cpu) {
                rc = topology_add_dev(cpu);
                if (rc)
-                       return rc;
+                       goto out;
        }
-       hotcpu_notifier(topology_cpu_callback, 0);
+       __hotcpu_notifier(topology_cpu_callback, 0);
 
-       return 0;
+out:
+       cpu_notifier_register_done();
+       return rc;
 }
 
 device_initcall(topology_sysfs_init);