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acpi-cpufreq: Fix CPU hotplug callback registration

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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>
This commit is contained in:
Srivatsa S. Bhat 2014-03-11 02:10:06 +05:30 committed by Rafael J. Wysocki
parent f0e71fcd0f
commit 0197fbd212
1 changed files with 4 additions and 3 deletions
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7
drivers/cpufreq/acpi-cpufreq.c
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@ -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();
}
}