acpi-cpufreq: 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 acpi-cpufreq code by using this latter form of callback registration.

Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.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/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 18448a7e9f8654e1560d2ec7eb354dd85ba094f4..245ae078e68ef4789f308a012ebd6abadafe6280 100644 (file)
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -907,15 +907,16 @@ static void __init acpi_cpufreq_boost_init(void)
 
                acpi_cpufreq_driver.boost_supported = true;
                acpi_cpufreq_driver.boost_enabled = boost_state(0);
-               get_online_cpus();
+
+               cpu_notifier_register_begin();
 
                /* Force all MSRs to the same value */
                boost_set_msrs(acpi_cpufreq_driver.boost_enabled,
                               cpu_online_mask);
 
-               register_cpu_notifier(&boost_nb);
+               __register_cpu_notifier(&boost_nb);
 
-               put_online_cpus();
+               cpu_notifier_register_done();
        }
 }