+/*
+ * Grace period handling:
+ * The grace period handling consists out of two steps:
+ * - A new grace period is started.
+ * This is done by rcu_start_batch. The start is not broadcasted to
+ * all cpus, they must pick this up by comparing rcu_ctrlblk.cur with
+ * RCU_quiescbatch(cpu). All cpus are recorded in the
+ * rcu_state.rcu_cpu_mask bitmap.
+ * - All cpus must go through a quiescent state.
+ * Since the start of the grace period is not broadcasted, at least two
+ * calls to rcu_check_quiescent_state are required:
+ * The first call just notices that a new grace period is running. The
+ * following calls check if there was a quiescent state since the beginning
+ * of the grace period. If so, it updates rcu_state.rcu_cpu_mask. If
+ * the bitmap is empty, then the grace period is completed.
+ * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
+ * period (if necessary).
+ */