| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 22/51] x86, intel, rapl: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:38:36 +0530 |
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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_maps_update_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_maps_update_done();
Fix the intel rapl code in x86 by using this latter form of callback registration.
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Paul Mackerras <paulus@samba.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: x86@kernel.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@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..bc41c02 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_maps_update_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_maps_update_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_maps_update_done(); return 0; }
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