x86, intel, cacheinfo: 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 intel cacheinfo 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>

1 files changed, 8 insertions, 5 deletions

diff --git a/arch/x86/kernel/cpu/intel_cacheinfo.c b/arch/x86/kernel/cpu/intel_cacheinfo.c
index 0641113e2965..a952e9c85b6f 100644
--- a/arch/x86/kernel/cpu/intel_cacheinfo.c
+++ b/arch/x86/kernel/cpu/intel_cacheinfo.c
@@ -1225,21 +1225,24 @@ static struct notifier_block cacheinfo_cpu_notifier = {
 
 static int __init cache_sysfs_init(void)
 {
-	int i;
+	int i, err = 0;
 
 	if (num_cache_leaves == 0)
 		return 0;
 
+	cpu_notifier_register_begin();
 	for_each_online_cpu(i) {
-		int err;
 		struct device *dev = get_cpu_device(i);
 
 		err = cache_add_dev(dev);
 		if (err)
-			return err;
+			goto out;
 	}
-	register_hotcpu_notifier(&cacheinfo_cpu_notifier);
-	return 0;
+	__register_hotcpu_notifier(&cacheinfo_cpu_notifier);
+
+out:
+	cpu_notifier_register_done();
+	return err;
 }
 
 device_initcall(cache_sysfs_init);