Commit eff722b0 authored Mar 11, 2014 by Srivatsa S. Bhat Committed by Rafael J. Wysocki Mar 20, 2014

ia64, salinfo: Fix 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 salinfo 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>

parent f0bdb5e0

arch/ia64/kernel/salinfo.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -635,6 +635,8 @@ salinfo_init(void)
		(void *)salinfo_entries[i].feature);
		}

		cpu_notifier_register_begin();

		for (i = 0; i < ARRAY_SIZE(salinfo_log_name); i++) {
		data = salinfo_data + i;
		data->type = i;
		@@ -669,7 +671,9 @@ salinfo_init(void)
		salinfo_timer.function = &salinfo_timeout;
		add_timer(&salinfo_timer);

		register_hotcpu_notifier(&salinfo_cpu_notifier);
		__register_hotcpu_notifier(&salinfo_cpu_notifier);

		cpu_notifier_register_done();

		return 0;
		}