+/*
+ * Trace-event helper function for rcu_start_future_gp() and
+ * rcu_nocb_wait_gp().
+ */
+static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
+ unsigned long c, char *s)
+{
+ trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
+ rnp->completed, c, rnp->level,
+ rnp->grplo, rnp->grphi, s);
+}
+
+/*
+ * Start some future grace period, as needed to handle newly arrived
+ * callbacks. The required future grace periods are recorded in each
+ * rcu_node structure's ->need_future_gp field.
+ *
+ * The caller must hold the specified rcu_node structure's ->lock.
+ */
+static unsigned long __maybe_unused
+rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp)
+{
+ unsigned long c;
+ int i;
+ struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
+
+ /*
+ * Pick up grace-period number for new callbacks. If this
+ * grace period is already marked as needed, return to the caller.
+ */
+ c = rcu_cbs_completed(rdp->rsp, rnp);
+ trace_rcu_future_gp(rnp, rdp, c, "Startleaf");
+ if (rnp->need_future_gp[c & 0x1]) {
+ trace_rcu_future_gp(rnp, rdp, c, "Prestartleaf");
+ return c;
+ }
+
+ /*
+ * If either this rcu_node structure or the root rcu_node structure
+ * believe that a grace period is in progress, then we must wait
+ * for the one following, which is in "c". Because our request
+ * will be noticed at the end of the current grace period, we don't
+ * need to explicitly start one.
+ */
+ if (rnp->gpnum != rnp->completed ||
+ ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) {
+ rnp->need_future_gp[c & 0x1]++;
+ trace_rcu_future_gp(rnp, rdp, c, "Startedleaf");
+ return c;
+ }
+
+ /*
+ * There might be no grace period in progress. If we don't already
+ * hold it, acquire the root rcu_node structure's lock in order to
+ * start one (if needed).
+ */
+ if (rnp != rnp_root)
+ raw_spin_lock(&rnp_root->lock);
+
+ /*
+ * Get a new grace-period number. If there really is no grace
+ * period in progress, it will be smaller than the one we obtained
+ * earlier. Adjust callbacks as needed. Note that even no-CBs
+ * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
+ */
+ c = rcu_cbs_completed(rdp->rsp, rnp_root);
+ for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
+ if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
+ rdp->nxtcompleted[i] = c;
+
+ /*
+ * If the needed for the required grace period is already
+ * recorded, trace and leave.
+ */
+ if (rnp_root->need_future_gp[c & 0x1]) {
+ trace_rcu_future_gp(rnp, rdp, c, "Prestartedroot");
+ goto unlock_out;
+ }
+
+ /* Record the need for the future grace period. */
+ rnp_root->need_future_gp[c & 0x1]++;
+
+ /* If a grace period is not already in progress, start one. */
+ if (rnp_root->gpnum != rnp_root->completed) {
+ trace_rcu_future_gp(rnp, rdp, c, "Startedleafroot");
+ } else {
+ trace_rcu_future_gp(rnp, rdp, c, "Startedroot");
+ rcu_start_gp(rdp->rsp);
+ }
+unlock_out:
+ if (rnp != rnp_root)
+ raw_spin_unlock(&rnp_root->lock);
+ return c;
+}
+
+/*
+ * Clean up any old requests for the just-ended grace period. Also return
+ * whether any additional grace periods have been requested. Also invoke
+ * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
+ * waiting for this grace period to complete.
+ */
+static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
+{
+ int c = rnp->completed;
+ int needmore;
+ struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
+
+ rcu_nocb_gp_cleanup(rsp, rnp);
+ rnp->need_future_gp[c & 0x1] = 0;
+ needmore = rnp->need_future_gp[(c + 1) & 0x1];
+ trace_rcu_future_gp(rnp, rdp, c, needmore ? "CleanupMore" : "Cleanup");
+ return needmore;
+}
+