arm: perf: fold hotplug notifier into arm_pmu

Handling multiple PMUs using a single hotplug notifier requires a list
of PMUs to be maintained, with synchronisation in the probe, remove, and
notify paths. This is error-prone and makes the code much harder to
maintain.

Instead of using a single notifier, we can dynamically allocate a
notifier block per-PMU. The end result is the same, but the list of PMUs
is implicit in the hotplug notifier list rather than within a perf-local
data structure, which makes the code far easier to handle.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

2 files changed, 35 insertions, 35 deletions

diff --git a/arch/arm/include/asm/pmu.h b/arch/arm/include/asm/pmu.h
index cc0149835507..b1596bd59129 100644
--- a/arch/arm/include/asm/pmu.h
+++ b/arch/arm/include/asm/pmu.h
@@ -116,6 +116,7 @@ struct arm_pmu {
         u64             max_period;
         struct platform_device  *plat_device;
         struct pmu_hw_events    __percpu *hw_events;
+        struct notifier_block   hotplug_nb;
 };
 
 #define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))
diff --git a/arch/arm/kernel/perf_event_cpu.c b/arch/arm/kernel/perf_event_cpu.c
index f0f6c5ef41b0..dd9acc95ebc0 100644
--- a/arch/arm/kernel/perf_event_cpu.c
+++ b/arch/arm/kernel/perf_event_cpu.c
@@ -160,8 +160,31 @@ static int cpu_pmu_request_irq(struct arm_pmu *cpu_pmu, irq_handler_t handler)
         return 0;
 }
 
+/*
+ * 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 cpu_pmu_notify(struct notifier_block *b, unsigned long action,
+                          void *hcpu)
+{
+        struct arm_pmu *pmu = container_of(b, struct arm_pmu, hotplug_nb);
+
+        if ((action & ~CPU_TASKS_FROZEN) != CPU_STARTING)
+                return NOTIFY_DONE;
+
+        if (pmu->reset)
+                pmu->reset(pmu);
+        else
+                return NOTIFY_DONE;
+
+        return NOTIFY_OK;
+}
+
 static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
 {
+        int err;
         int cpu;
         struct pmu_hw_events __percpu *cpu_hw_events;
 
@@ -169,6 +192,11 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
         if (!cpu_hw_events)
                 return -ENOMEM;
 
+        cpu_pmu->hotplug_nb.notifier_call = cpu_pmu_notify;
+        err = register_cpu_notifier(&cpu_pmu->hotplug_nb);
+        if (err)
+                goto out_hw_events;
+
         for_each_possible_cpu(cpu) {
                 struct pmu_hw_events *events = per_cpu_ptr(cpu_hw_events, cpu);
                 raw_spin_lock_init(&events->pmu_lock);
@@ -188,38 +216,19 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
                 cpu_pmu->pmu.capabilities |= PERF_PMU_CAP_NO_INTERRUPT;
 
         return 0;
+
+out_hw_events:
+        free_percpu(cpu_hw_events);
+        return err;
 }
 
 static void cpu_pmu_destroy(struct arm_pmu *cpu_pmu)
 {
+        unregister_cpu_notifier(&cpu_pmu->hotplug_nb);
         free_percpu(cpu_pmu->hw_events);
 }
 
 /*
- * 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 cpu_pmu_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(cpu_pmu);
-        else
-                return NOTIFY_DONE;
-
-        return NOTIFY_OK;
-}
-
-static struct notifier_block cpu_pmu_hotplug_notifier = {
-        .notifier_call = cpu_pmu_notify,
-};
-
-/*
  * PMU platform driver and devicetree bindings.
  */
 static struct of_device_id cpu_pmu_of_device_ids[] = {
@@ -344,16 +353,6 @@ static struct platform_driver cpu_pmu_driver = {
 
 static int __init register_pmu_driver(void)
 {
-        int err;
-
-        err = register_cpu_notifier(&cpu_pmu_hotplug_notifier);
-        if (err)
-                return err;
-
-        err = platform_driver_register(&cpu_pmu_driver);
-        if (err)
-                unregister_cpu_notifier(&cpu_pmu_hotplug_notifier);
-
-        return err;
+        return platform_driver_register(&cpu_pmu_driver);
 }
 device_initcall(register_pmu_driver);