sparc, sysfs: 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 sysfs code in sparc by using this latter form of callback
registration.

Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
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/sparc/kernel/sysfs.c b/arch/sparc/kernel/sysfs.c
index c21c673e5f7cde71cdeca0c4b48bf565df96bfd7..a364000ca1aa8a495f7e8b9bf59882350f41c6de 100644 (file)
--- a/arch/sparc/kernel/sysfs.c
+++ b/arch/sparc/kernel/sysfs.c
@@ -300,7 +300,7 @@ static int __init topology_init(void)
 
        check_mmu_stats();
 
-       register_cpu_notifier(&sysfs_cpu_nb);
+       cpu_notifier_register_begin();
 
        for_each_possible_cpu(cpu) {
                struct cpu *c = &per_cpu(cpu_devices, cpu);
@@ -310,6 +310,10 @@ static int __init topology_init(void)
                        register_cpu_online(cpu);
        }
 
+       __register_cpu_notifier(&sysfs_cpu_nb);
+
+       cpu_notifier_register_done();
+
        return 0;
 }