[PATCH v2 24/52] x86, intel, rapl: Fix CPU hotplug callback registration

[Srivatsa S. Bhat]

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 rapl code in x86 by using this latter form of callback
registration.

Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Paul Mackerras <pau...@samba.org>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Arnaldo Carvalho de Melo <a...@ghostprotocols.net>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: x...@kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---

 arch/x86/kernel/cpu/perf_event_intel_rapl.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_rapl.c 
b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
index 5ad35ad..059218e 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_rapl.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_rapl.c
@@ -646,19 +646,20 @@ static int __init rapl_pmu_init(void)
                /* unsupported */
                return 0;
        }
-       get_online_cpus();
+
+       cpu_notifier_register_begin();
 
        for_each_online_cpu(cpu) {
                rapl_cpu_prepare(cpu);
                rapl_cpu_init(cpu);
        }
 
-       perf_cpu_notifier(rapl_cpu_notifier);
+       __perf_cpu_notifier(rapl_cpu_notifier);
 
        ret = perf_pmu_register(&rapl_pmu_class, "power", -1);
        if (WARN_ON(ret)) {
                pr_info("RAPL PMU detected, registration failed (%d), RAPL PMU 
disabled\n", ret);
-               put_online_cpus();
+               cpu_notifier_register_done();
                return -1;
        }
 
@@ -672,7 +673,7 @@ static int __init rapl_pmu_init(void)
                hweight32(rapl_cntr_mask),
                ktime_to_ms(pmu->timer_interval));
 
-       put_online_cpus();
+       cpu_notifier_register_done();
 
        return 0;
 }

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