+static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
+
+static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
+ .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
+ .dynticks = ATOMIC_INIT(1),
+#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
+ .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
+ .dynticks_idle = ATOMIC_INIT(1),
+#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+};
+
+/*
+ * Let the RCU core know that this CPU has gone through the scheduler,
+ * which is a quiescent state. This is called when the need for a
+ * quiescent state is urgent, so we burn an atomic operation and full
+ * memory barriers to let the RCU core know about it, regardless of what
+ * this CPU might (or might not) do in the near future.
+ *
+ * We inform the RCU core by emulating a zero-duration dyntick-idle
+ * period, which we in turn do by incrementing the ->dynticks counter
+ * by two.
+ */
+static void rcu_momentary_dyntick_idle(void)
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+ struct rcu_dynticks *rdtp;
+ int resched_mask;
+ struct rcu_state *rsp;
+
+ local_irq_save(flags);
+
+ /*
+ * Yes, we can lose flag-setting operations. This is OK, because
+ * the flag will be set again after some delay.
+ */
+ resched_mask = raw_cpu_read(rcu_sched_qs_mask);
+ raw_cpu_write(rcu_sched_qs_mask, 0);
+
+ /* Find the flavor that needs a quiescent state. */
+ for_each_rcu_flavor(rsp) {
+ rdp = raw_cpu_ptr(rsp->rda);
+ if (!(resched_mask & rsp->flavor_mask))
+ continue;
+ smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */
+ if (ACCESS_ONCE(rdp->mynode->completed) !=
+ ACCESS_ONCE(rdp->cond_resched_completed))
+ continue;
+
+ /*
+ * Pretend to be momentarily idle for the quiescent state.
+ * This allows the grace-period kthread to record the
+ * quiescent state, with no need for this CPU to do anything
+ * further.
+ */
+ rdtp = this_cpu_ptr(&rcu_dynticks);
+ smp_mb__before_atomic(); /* Earlier stuff before QS. */
+ atomic_add(2, &rdtp->dynticks); /* QS. */
+ smp_mb__after_atomic(); /* Later stuff after QS. */
+ break;
+ }
+ local_irq_restore(flags);
+}
+