x86, amd, 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 amd-uncore code in 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_amd_uncore.c b/arch/x86/kernel/cpu/perf_event_amd_uncore.c
index 754291adec338b34317d5c07a359741e5e298d80..3bbdf4cd38b9c4e38dcf8e4f480753e93858631a 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_amd_uncore.c
+++ b/arch/x86/kernel/cpu/perf_event_amd_uncore.c
@@ -531,15 +531,16 @@ static int __init amd_uncore_init(void)
        if (ret)
                return -ENODEV;
 
-       get_online_cpus();
+       cpu_notifier_register_begin();
+
        /* init cpus already online before registering for hotplug notifier */
        for_each_online_cpu(cpu) {
                amd_uncore_cpu_up_prepare(cpu);
                smp_call_function_single(cpu, init_cpu_already_online, NULL, 1);
        }
 
-       register_cpu_notifier(&amd_uncore_cpu_notifier_block);
-       put_online_cpus();
+       __register_cpu_notifier(&amd_uncore_cpu_notifier_block);
+       cpu_notifier_register_done();
 
        return 0;
 }