+static void swevent_hlist_release_rcu(struct rcu_head *rcu_head)
+{
+ struct swevent_hlist *hlist;
+
+ hlist = container_of(rcu_head, struct swevent_hlist, rcu_head);
+ kfree(hlist);
+}
+
+static void swevent_hlist_release(struct perf_cpu_context *cpuctx)
+{
+ struct swevent_hlist *hlist;
+
+ if (!cpuctx->swevent_hlist)
+ return;
+
+ hlist = cpuctx->swevent_hlist;
+ rcu_assign_pointer(cpuctx->swevent_hlist, NULL);
+ call_rcu(&hlist->rcu_head, swevent_hlist_release_rcu);
+}
+
+static void swevent_hlist_put_cpu(struct perf_event *event, int cpu)
+{
+ struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
+
+ mutex_lock(&cpuctx->hlist_mutex);
+
+ if (!--cpuctx->hlist_refcount)
+ swevent_hlist_release(cpuctx);
+
+ mutex_unlock(&cpuctx->hlist_mutex);
+}
+
+static void swevent_hlist_put(struct perf_event *event)
+{
+ int cpu;
+
+ if (event->cpu != -1) {
+ swevent_hlist_put_cpu(event, event->cpu);
+ return;
+ }
+
+ for_each_possible_cpu(cpu)
+ swevent_hlist_put_cpu(event, cpu);
+}
+
+static int swevent_hlist_get_cpu(struct perf_event *event, int cpu)
+{
+ struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
+ int err = 0;
+
+ mutex_lock(&cpuctx->hlist_mutex);
+
+ if (!cpuctx->swevent_hlist && cpu_online(cpu)) {
+ struct swevent_hlist *hlist;
+
+ hlist = kzalloc(sizeof(*hlist), GFP_KERNEL);
+ if (!hlist) {
+ err = -ENOMEM;
+ goto exit;
+ }
+ rcu_assign_pointer(cpuctx->swevent_hlist, hlist);
+ }
+ cpuctx->hlist_refcount++;
+ exit:
+ mutex_unlock(&cpuctx->hlist_mutex);
+
+ return err;
+}
+
+static int swevent_hlist_get(struct perf_event *event)
+{
+ int err;
+ int cpu, failed_cpu;
+
+ if (event->cpu != -1)
+ return swevent_hlist_get_cpu(event, event->cpu);
+
+ get_online_cpus();
+ for_each_possible_cpu(cpu) {
+ err = swevent_hlist_get_cpu(event, cpu);
+ if (err) {
+ failed_cpu = cpu;
+ goto fail;
+ }
+ }
+ put_online_cpus();
+
+ return 0;
+ fail:
+ for_each_possible_cpu(cpu) {
+ if (cpu == failed_cpu)
+ break;
+ swevent_hlist_put_cpu(event, cpu);
+ }
+
+ put_online_cpus();
+ return err;
+}
+
+#ifdef CONFIG_EVENT_TRACING