x86, intel, uncore: 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 uncore code in intel-x86 by using this latter form of callback
registration.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
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/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
index 047f540cf3f71cfe03f69d796a1957b8a58caebc..28922f62eb2990be0552802c3c3630ec2a354d8d 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_intel_uncore.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
@@ -3817,7 +3817,7 @@ static int __init uncore_cpu_init(void)
        if (ret)
                return ret;
 
-       get_online_cpus();
+       cpu_notifier_register_begin();
 
        for_each_online_cpu(cpu) {
                int i, phys_id = topology_physical_package_id(cpu);
@@ -3836,9 +3836,9 @@ static int __init uncore_cpu_init(void)
        }
        on_each_cpu(uncore_cpu_setup, NULL, 1);
 
-       register_cpu_notifier(&uncore_cpu_nb);
+       __register_cpu_notifier(&uncore_cpu_nb);
 
-       put_online_cpus();
+       cpu_notifier_register_done();
 
        return 0;
 }