Revert "rcu: Simplify rcu_init_nohz() cpumask handling"

This reverts commit 98ec984.

Author: paulmckrcu

kernel/rcu/tree_nocb.h

@@ -1210,34 +1210,45 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
 void __init rcu_init_nohz(void)
 {
 	int cpu;
+	bool need_rcu_nocb_mask = false;
+	bool offload_all = false;
 	struct rcu_data *rdp;
-	const struct cpumask *cpumask = NULL;
-
-#if defined(CONFIG_NO_HZ_FULL)
-	if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
-		cpumask = tick_nohz_full_mask;
-#endif
 
 #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
-	if (!rcu_state.nocb_is_setup && !cpumask)
-		cpumask = cpu_possible_mask;
-#endif
+	if (!rcu_state.nocb_is_setup) {
+		need_rcu_nocb_mask = true;
+		offload_all = true;
+	}
+#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */
+
+#if defined(CONFIG_NO_HZ_FULL)
+	if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {
+		need_rcu_nocb_mask = true;
+		offload_all = false; /* NO_HZ_FULL has its own mask. */
+	}
+#endif /* #if defined(CONFIG_NO_HZ_FULL) */
 
-	if (cpumask) {
+	if (need_rcu_nocb_mask) {
 		if (!cpumask_available(rcu_nocb_mask)) {
 			if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
 				pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
 				return;
 			}
 		}
-
-		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
 		rcu_state.nocb_is_setup = true;
 	}
 
 	if (!rcu_state.nocb_is_setup)
 		return;
 
+#if defined(CONFIG_NO_HZ_FULL)
+	if (tick_nohz_full_running)
+		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
+#endif /* #if defined(CONFIG_NO_HZ_FULL) */
+
+	if (offload_all)
+		cpumask_setall(rcu_nocb_mask);
+
 	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
 		pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
 		cpumask_and(rcu_nocb_mask, cpu_possible_mask,