Perf: arm64: fix disable of pmu irq during hotplug

PMU irq is disabled when a cpu is hotplugged off
and perf is running. Using cpu_pmu->active_events
to determine if the pmu is running left a window
where it is decremented to 0 in hw_perf_event_destroy,
and then armpmu_release_hardware is called. If a cpu
is hotplugged off in this window it may not disable
its irq. Use a separate flag which is not cleared
until after the irq is released by all online cpus.

The variable needs to be tristate because of the possibility
of a cpu being hotplugged in during this window. In that
case it should not enable its irq when the pmu is being
shut down. Having the GOING_DOWN state allows correct
behavior for cpus both going down and coming up.

Change-Id: I934ba5dec34e681ce8defd7fa7e311b4a2a92c1a
Signed-off-by: Neil Leeder <nleeder@codeaurora.org>
[satyap: merge conflict resolution and move changes in
         arch/arm64/kernel/perf_event.c to drivers/perf/arm_pmu.c
         to align with kernel 4.4]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>

arch/arm64/kernel/perf_debug.c

@@ -30,6 +30,7 @@ static char *descriptions =
 	" 7 Perf: arm64: Update PMU force reset\n"
 	"10 Perf: arm64: tracectr: initialize counts after hotplug\n"
 	"11 Perf: arm64: Refine disable/enable in tracecounters\n"
+	"12 Perf: arm64: fix disable of pmu irq during hotplug\n"
 	"15 Perf: arm64: make debug dir handle exportable\n"
 	"16 Perf: arm64: add perf trace user\n"
 	"17 Perf: arm64: add support for kryo pmu\n"

drivers/perf/arm_pmu.c

@@ -370,6 +370,8 @@ armpmu_reserve_hardware(struct arm_pmu *armpmu)
 		return err;
 	}
 
+	armpmu->pmu_state = ARM_PMU_STATE_RUNNING;
+
 	return 0;
 }
 
@@ -630,6 +632,14 @@ static void cpu_pmu_free_irq(struct arm_pmu *cpu_pmu)
 	struct pmu_hw_events __percpu *hw_events = cpu_pmu->hw_events;
 
 	irqs = min(pmu_device->num_resources, num_possible_cpus());
+	if (!irqs)
+		return;
+
+	/*
+	 * If a cpu comes online during this function, do not enable its irq.
+	 * If a cpu goes offline, it should disable its irq.
+	 */
+	cpu_pmu->pmu_state = ARM_PMU_STATE_GOING_DOWN;
 
 	irq = platform_get_irq(pmu_device, 0);
 	if (irq >= 0 && irq_is_percpu(irq)) {
@@ -649,6 +659,7 @@ static void cpu_pmu_free_irq(struct arm_pmu *cpu_pmu)
 				free_irq(irq, per_cpu_ptr(&hw_events->percpu_pmu, cpu));
 		}
 	}
+	cpu_pmu->pmu_state = ARM_PMU_STATE_OFF;
 }
 
 static int cpu_pmu_request_irq(struct arm_pmu *cpu_pmu, irq_handler_t handler)
@@ -766,7 +777,6 @@ static int cpu_pmu_notify(struct notifier_block *b, unsigned long action,
 	struct arm_pmu *cpu_pmu = container_of(b, struct arm_pmu, hotplug_nb);
 	int irq;
 	struct pmu *pmu;
-	int perf_running;
 	unsigned long masked_action = action & ~CPU_TASKS_FROZEN;
 	int ret = NOTIFY_DONE;
 
@@ -783,13 +793,12 @@ static int cpu_pmu_notify(struct notifier_block *b, unsigned long action,
 	if (!cpumask_test_cpu(cpu, &cpu_pmu->supported_cpus))
 		return NOTIFY_DONE;
 
-	perf_running = atomic_read(&cpu_pmu->active_events);
 	switch (masked_action) {
 	case CPU_DOWN_PREPARE:
 		if (cpu_pmu->save_pm_registers)
 			smp_call_function_single(cpu,
 				cpu_pmu->save_pm_registers, hcpu, 1);
-		if (perf_running) {
+		if (cpu_pmu->pmu_state != ARM_PMU_STATE_OFF) {
 			if (cpu_has_active_perf(cpu, cpu_pmu))
 				smp_call_function_single(cpu,
 					armpmu_update_counters, cpu_pmu, 1);
@@ -808,7 +817,7 @@ static int cpu_pmu_notify(struct notifier_block *b, unsigned long action,
 			cpu_pmu->reset(NULL);
 		if (cpu_pmu->restore_pm_registers)
 			cpu_pmu->restore_pm_registers(hcpu);
-		if (perf_running) {
+		if (cpu_pmu->pmu_state == ARM_PMU_STATE_RUNNING) {
 			/* Arm the PMU IRQ before appearing. */
 			if (cpu_pmu->plat_device) {
 				irq = cpu_pmu->percpu_irq;

include/linux/perf/arm_pmu.h

@@ -51,6 +51,12 @@ struct arm_pmu_platdata {
 	},								\
 }
 
+enum arm_pmu_state {
+	ARM_PMU_STATE_OFF       = 0,
+	ARM_PMU_STATE_GOING_DOWN,
+	ARM_PMU_STATE_RUNNING,
+};
+
 /* The events for a given PMU register set. */
 struct pmu_hw_events {
 	/*
@@ -103,6 +109,7 @@ struct arm_pmu {
 	void		(*free_irq)(struct arm_pmu *);
 	int		(*map_event)(struct perf_event *event);
 	int		num_events;
+	int		pmu_state;
 	int		percpu_irq;
 	atomic_t	active_events;
 	struct mutex	reserve_mutex;