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>

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index da85a8e830a12d65e9d2f8a7f1db39b5477e9e85..d89382be899dde8d84c33357cad117ac2efc2357 100644 (file)
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -943,12 +943,14 @@ static __init int hpet_late_init(void)
        if (boot_cpu_has(X86_FEATURE_ARAT))
                return 0;
 
+       cpu_notifier_register_begin();
        for_each_online_cpu(cpu) {
                hpet_cpuhp_notify(NULL, CPU_ONLINE, (void *)(long)cpu);
        }
 
        /* 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;
 }