}
smpboot_park_threads(cpu);
+ /*
+ * By now we've cleared cpu_active_mask, wait for all preempt-disabled
+ * and RCU users of this state to go away such that all new such users
+ * will observe it.
+ *
+ * For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
+ * not imply sync_sched(), so explicitly call both.
+ */
+#ifdef CONFIG_PREEMPT
+ synchronize_sched();
+#endif
+ synchronize_rcu();
+
+ /*
+ * So now all preempt/rcu users must observe !cpu_active().
+ */
+
err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
if (err) {
/* CPU didn't die: tell everyone. Can't complain. */