---

yaml
---
r: 288323
b: refs/heads/master
c: a0feb6d
h: refs/heads/master
i:
  288321: a22d1a1
  288319: 7f8245b
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 3f31ae121348afd9ed39700ea2a63c17cd7eeed1
+refs/heads/master: a0feb6db0fe03326d7d2c7a4615ce3289615c023

trunk/arch/arm/kernel/perf_event.c

@@ -679,6 +679,28 @@ static void __init cpu_pmu_init(struct arm_pmu *armpmu)
 	armpmu->type = ARM_PMU_DEVICE_CPU;
 }
 
+/*
+ * PMU hardware loses all context when a CPU goes offline.
+ * When a CPU is hotplugged back in, since some hardware registers are
+ * UNKNOWN at reset, the PMU must be explicitly reset to avoid reading
+ * junk values out of them.
+ */
+static int __cpuinit pmu_cpu_notify(struct notifier_block *b,
+					unsigned long action, void *hcpu)
+{
+	if ((action & ~CPU_TASKS_FROZEN) != CPU_STARTING)
+		return NOTIFY_DONE;
+
+	if (cpu_pmu && cpu_pmu->reset)
+		cpu_pmu->reset(NULL);
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata pmu_cpu_notifier = {
+	.notifier_call = pmu_cpu_notify,
+};
+
 /*
  * CPU PMU identification and registration.
  */
@@ -730,6 +752,7 @@ init_hw_perf_events(void)
 		pr_info("enabled with %s PMU driver, %d counters available\n",
 			cpu_pmu->name, cpu_pmu->num_events);
 		cpu_pmu_init(cpu_pmu);
+		register_cpu_notifier(&pmu_cpu_notifier);
 		armpmu_register(cpu_pmu, "cpu", PERF_TYPE_RAW);
 	} else {
 		pr_info("no hardware support available\n");