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arm64, debug-monitors: 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 debug-monitors code in arm64 by using this latter form of callback
registration.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Will Deacon <will.deacon@arm.com>
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 02:09:20 +05:30 committed by Rafael J. Wysocki
parent 3d0dc643f8
commit 4b0b68af37
1 changed files with 5 additions and 1 deletions
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6
arch/arm64/kernel/debug-monitors.c
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@ -155,12 +155,16 @@ static struct notifier_block os_lock_nb = {
static int debug_monitors_init(void)
{
cpu_notifier_register_begin();
/* Clear the OS lock. */
smp_call_function(clear_os_lock, NULL, 1);
clear_os_lock(NULL);
/* Register hotplug handler. */
register_cpu_notifier(&os_lock_nb);
__register_cpu_notifier(&os_lock_nb);
cpu_notifier_register_done();
return 0;
}
postcore_initcall(debug_monitors_init);