s390, cacheinfo: 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 cacheinfo code in s390 by using this latter form of callback
registration.

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.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/s390/kernel/cache.c b/arch/s390/kernel/cache.c
index 3a414c0f93edcd08d69d3a1aa2af645c098327c9..c0b03c28d15717448f4f713c083bbd891861f42b 100644 (file)
--- a/arch/s390/kernel/cache.c
+++ b/arch/s390/kernel/cache.c
@@ -378,9 +378,12 @@ static int __init cache_init(void)
        if (!test_facility(34))
                return 0;
        cache_build_info();
+
+       cpu_notifier_register_begin();
        for_each_online_cpu(cpu)
                cache_add_cpu(cpu);
-       hotcpu_notifier(cache_hotplug, 0);
+       __hotcpu_notifier(cache_hotplug, 0);
+       cpu_notifier_register_done();
        return 0;
 }
 device_initcall(cache_init);