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clocksource, dummy-timer: 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 clocksource dummy-timer code by using this latter form of callback
registration.

Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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>
This commit is contained in:
Srivatsa S. Bhat 2014-03-11 02:10:23 +05:30 committed by Rafael J. Wysocki
parent e12b711196
commit 8daa127f4e
1 changed files with 8 additions and 3 deletions
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11
drivers/clocksource/dummy_timer.c
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@ -56,14 +56,19 @@ static struct notifier_block dummy_timer_cpu_nb = {
static int __init dummy_timer_register(void)
{
int err = register_cpu_notifier(&dummy_timer_cpu_nb);
int err = 0;
cpu_notifier_register_begin();
err = __register_cpu_notifier(&dummy_timer_cpu_nb);
if (err)
return err;
goto out;
/* We won't get a call on the boot CPU, so register immediately */
if (num_possible_cpus() > 1)
dummy_timer_setup();
return 0;
out:
cpu_notifier_register_done();
return err;
}
early_initcall(dummy_timer_register);