Fix Arm system PMU hotplug issues

Like arm-cci, arm-ccn has the same issue of disabling preemption around operations which can take mutexes. Again, remove the definite bug by simply not trying to fight the theoretical races. And since we are touching the hotplug handling code, take the opportunity to streamline it, as there's really no need to store a full-sized cpumask to keep track of a single CPU ID.

Signed-off-by Robin Murphy <[email protected]>

---
  drivers/perf/arm-ccn.c | 25 +++++++++++++------------
  1 file changed, 13 insertions(+), 12 deletions(-)

drivers/perf/arm-ccn.c +11 -8

index 2ae76026e947..0bb52d9bdcf7 100644
@@ -167,7 +167,7 @@ struct arm_ccn_dt {
 
  	struct hrtimer hrtimer;
 
-	cpumask_t cpu;
+	unsigned int cpu;
  	struct hlist_node node;
 
  	struct pmu pmu;

@@ -559,7 +559,7 @@ static ssize_t arm_ccn_pmu_cpumask_show(struct device *dev,
  {
  	struct arm_ccn *ccn = pmu_to_arm_ccn(dev_get_drvdata(dev));
 
-	return cpumap_print_to_pagebuf(true, buf, &ccn->dt.cpu);
+	return cpumap_print_to_pagebuf(true, buf, cpumask_of(ccn->dt.cpu));
  }
 
  static struct device_attribute arm_ccn_pmu_cpumask_attr =

@@ -759,7 +759,7 @@ static int arm_ccn_pmu_event_init(struct perf_event *event)
  	 * mitigate this, we enforce CPU assignment to one, selected
  	 * processor (the one described in the "cpumask" attribute).
  	 */
-	event->cpu = cpumask_first(&ccn->dt.cpu);
+	event->cpu = ccn->dt.cpu;
 
  	node_xp = CCN_CONFIG_NODE(event->attr.config);
  	type = CCN_CONFIG_TYPE(event->attr.config);

@@ -1215,15 +1215,15 @@ static int arm_ccn_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
  	struct arm_ccn *ccn = container_of(dt, struct arm_ccn, dt);
  	unsigned int target;
 
-	if (!cpumask_test_and_clear_cpu(cpu, &dt->cpu))
+	if (cpu != dt->cpu)
  		return 0;
  	target = cpumask_any_but(cpu_online_mask, cpu);
  	if (target >= nr_cpu_ids)
  		return 0;
  	perf_pmu_migrate_context(&dt->pmu, cpu, target);
-	cpumask_set_cpu(target, &dt->cpu);
+	dt->cpu = target;
  	if (ccn->irq)
-		WARN_ON(irq_set_affinity_hint(ccn->irq, &dt->cpu) != 0);
+		WARN_ON(irq_set_affinity_hint(ccn->irq, cpumask_of(dt->cpu)));
  	return 0;
  }
 

@@ -1299,29 +1299,30 @@ static int arm_ccn_pmu_init(struct arm_ccn *ccn)
  	}
 
  	/* Pick one CPU which we will use to collect data from CCN... */
-	cpumask_set_cpu(get_cpu(), &ccn->dt.cpu);
+	ccn->dt.cpu = raw_smp_processor_id();
 
  	/* Also make sure that the overflow interrupt is handled by this CPU */
  	if (ccn->irq) {
-		err = irq_set_affinity_hint(ccn->irq, &ccn->dt.cpu);
+		err = irq_set_affinity_hint(ccn->irq, cpumask_of(ccn->dt.cpu));
  		if (err) {
  			dev_err(ccn->dev, "Failed to set interrupt affinity!\n");
  			goto error_set_affinity;
  		}
  	}
 
+	cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE,
+					 &ccn->dt.node);
+
  	err = perf_pmu_register(&ccn->dt.pmu, name, -1);
  	if (err)
  		goto error_pmu_register;
 

Quoted 81 lines · Robin Murphy

Like arm-cci, arm-ccn has the same issue of disabling preemption around operations which can take mutexes. Again, remove the definite bug by simply not trying to fight the theoretical races. And since we are touching the hotplug handling code, take the opportunity to streamline it, as there's really no need to store a full-sized cpumask to keep track of a single CPU ID.

Signed-off-by Robin Murphy <[email protected]>

---
  drivers/perf/arm-ccn.c | 25 +++++++++++++------------

  1 file changed, 13 insertions(+), 12 deletions(-)

drivers/perf/arm-ccn.c +2 -2

index 2ae76026e947..0bb52d9bdcf7 100644
@@ -167,7 +167,7 @@ struct arm_ccn_dt {
       struct hrtimer hrtimer;
-    cpumask_t cpu;
+    unsigned int cpu;
       struct hlist_node node;
       struct pmu pmu;

@@ -559,7 +559,7 @@ static ssize_t arm_ccn_pmu_cpumask_show(struct 
 device *dev,
   {
       struct arm_ccn *ccn = pmu_to_arm_ccn(dev_get_drvdata(dev));
-    return cpumap_print_to_pagebuf(true, buf, &ccn->dt.cpu);
+    return cpumap_print_to_pagebuf(true, buf, cpumask_of(ccn->dt.cpu));
   }

  static struct device_attribute arm_ccn_pmu_cpumask_attr =

drivers/perf/arm-ccn.c +9 -9

@@ -759,7 +759,7 @@ static int arm_ccn_pmu_event_init(struct 
 perf_event *event)
        * mitigate this, we enforce CPU assignment to one, selected
        * processor (the one described in the "cpumask" attribute).
        */
-    event->cpu = cpumask_first(&ccn->dt.cpu);
+    event->cpu = ccn->dt.cpu;
       node_xp = CCN_CONFIG_NODE(event->attr.config);
       type = CCN_CONFIG_TYPE(event->attr.config);

@@ -1215,15 +1215,15 @@ static int arm_ccn_pmu_offline_cpu(unsigned 
 int cpu, struct hlist_node *node)
       struct arm_ccn *ccn = container_of(dt, struct arm_ccn, dt);
       unsigned int target;
-    if (!cpumask_test_and_clear_cpu(cpu, &dt->cpu))
+    if (cpu != dt->cpu)
           return 0;
       target = cpumask_any_but(cpu_online_mask, cpu);
       if (target >= nr_cpu_ids)
           return 0;
       perf_pmu_migrate_context(&dt->pmu, cpu, target);
-    cpumask_set_cpu(target, &dt->cpu);
+    dt->cpu = target;
       if (ccn->irq)
-        WARN_ON(irq_set_affinity_hint(ccn->irq, &dt->cpu) != 0);
+        WARN_ON(irq_set_affinity_hint(ccn->irq, cpumask_of(dt->cpu)));
       return 0;
   }

@@ -1299,29 +1299,30 @@ static int arm_ccn_pmu_init(struct arm_ccn *ccn)
       }
       /* Pick one CPU which we will use to collect data from CCN... */
-    cpumask_set_cpu(get_cpu(), &ccn->dt.cpu);
+    ccn->dt.cpu = raw_smp_processor_id();
       /* Also make sure that the overflow interrupt is handled by this CPU */
       if (ccn->irq) {
-        err = irq_set_affinity_hint(ccn->irq, &ccn->dt.cpu);
+        err = irq_set_affinity_hint(ccn->irq, cpumask_of(ccn->dt.cpu));
           if (err) {
               dev_err(ccn->dev, "Failed to set interrupt affinity!\n");
               goto error_set_affinity;
           }
       }
+    cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE,
+                     &ccn->dt.node);
+
       err = perf_pmu_register(&ccn->dt.pmu, name, -1);
       if (err)
           goto error_pmu_register;
-    cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE,
-                     &ccn->dt.node);
-    put_cpu();
       return 0;

Quoted 5 lines

  error_pmu_register:
+    cpuhp_state_remove_instance_nocalls(CPUHP_AP_PERF_ARM_CCN_ONLINE, +                        &ccn->dt.node); error_set_affinity:
-    put_cpu();

Super minor nit: We don't need the error_set_affinity label anymore, as we don't do anything here. Otherwise:

Reviewed-by Suzuki K Poulose <[email protected]>