x86, therm_throt.c: 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 thermal throttle code in x86 by using this latter form of callback
registration.

Cc: Tony Luck <tony.luck@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
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/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
index 3eec7de76efbb4650ea760f5163d495f47fd1f1d..e05dfa398dc294ed716a9d1beb3a6d1fd902e781 100644 (file)
--- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
+++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
@@ -319,7 +319,7 @@ static __init int thermal_throttle_init_device(void)
        if (!atomic_read(&therm_throt_en))
                return 0;
 
-       register_hotcpu_notifier(&thermal_throttle_cpu_notifier);
+       cpu_notifier_register_begin();
 
 #ifdef CONFIG_HOTPLUG_CPU
        mutex_lock(&therm_cpu_lock);
@@ -333,6 +333,9 @@ static __init int thermal_throttle_init_device(void)
        mutex_unlock(&therm_cpu_lock);
 #endif
 
+       __register_hotcpu_notifier(&thermal_throttle_cpu_notifier);
+       cpu_notifier_register_done();
+
        return 0;
 }
 device_initcall(thermal_throttle_init_device);