- * At this stage, only low level arch entry code remains and
- * then we'll run in userspace. We can assume there won't be
- * any RCU read-side critical section until the next call to
- * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency
- * on the tick.
+ * Even if context tracking is disabled on this CPU, because it's outside
+ * the full dynticks mask for example, we still have to keep track of the
+ * context transitions and states to prevent inconsistency on those of
+ * other CPUs.
+ * If a task triggers an exception in userspace, sleep on the exception
+ * handler and then migrate to another CPU, that new CPU must know where
+ * the exception returns by the time we call exception_exit().
+ * This information can only be provided by the previous CPU when it called
+ * exception_enter().
+ * OTOH we can spare the calls to vtime and RCU when context_tracking.active
+ * is false because we know that CPU is not tickless.