Commit 9014ad2a authored Mar 11, 2014 by Srivatsa S. Bhat Committed by Rafael J. Wysocki Mar 20, 2014

x86, hpet: 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 hpet code in x86 by using this latter form of callback registration.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

parent a8c17c29

arch/x86/kernel/hpet.c

+3 −1

Original line number	Original line	Diff line number	Diff line
	@@ -943,12 +943,14 @@ static __init int hpet_late_init(void)
	if (boot_cpu_has(X86_FEATURE_ARAT))		if (boot_cpu_has(X86_FEATURE_ARAT))
	return 0;		return 0;

			cpu_notifier_register_begin();
	for_each_online_cpu(cpu) {		for_each_online_cpu(cpu) {
	hpet_cpuhp_notify(NULL, CPU_ONLINE, (void *)(long)cpu);		hpet_cpuhp_notify(NULL, CPU_ONLINE, (void *)(long)cpu);
	}		}

	/* This notifier should be called after workqueue is ready */		/* This notifier should be called after workqueue is ready */
	hotcpu_notifier(hpet_cpuhp_notify, -20);		__hotcpu_notifier(hpet_cpuhp_notify, -20);
			cpu_notifier_register_done();

	return 0;		return 0;
	}		}