srcu: Allow SRCU to access rcu_scheduler_active

This is primarily a code-movement commit in preparation for allowing
SRCU to handle early-boot SRCU grace periods.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

include/linux/rcutiny.h

@@ -217,14 +217,14 @@ static inline void exit_rcu(void)
 {
 }
 
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU)
 extern int rcu_scheduler_active __read_mostly;
 void rcu_scheduler_starting(void);
-#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#else /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 static inline void rcu_scheduler_starting(void)
 {
 }
-#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#endif /* #else #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 
 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
 

kernel/rcu/tiny_plugin.h

@@ -52,7 +52,7 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = {
 	RCU_TRACE(.name = "rcu_bh")
 };
 
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU)
 #include <linux/kernel_stat.h>
 
 int rcu_scheduler_active __read_mostly;
@@ -65,15 +65,16 @@ EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  * to RCU_SCHEDULER_RUNNING, skipping the RCU_SCHEDULER_INIT stage.
  * The reason for this is that Tiny RCU does not need kthreads, so does
  * not have to care about the fact that the scheduler is half-initialized
- * at a certain phase of the boot process.
+ * at a certain phase of the boot process.  Unless SRCU is in the mix.
  */
 void __init rcu_scheduler_starting(void)
 {
 	WARN_ON(nr_context_switches() > 0);
-	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
+	rcu_scheduler_active = IS_ENABLED(CONFIG_SRCU)
+		? RCU_SCHEDULER_INIT : RCU_SCHEDULER_RUNNING;
 }
 
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SRCU) */
 
 #ifdef CONFIG_RCU_TRACE
 

kernel/rcu/tree.c

@@ -3974,7 +3974,7 @@ early_initcall(rcu_spawn_gp_kthread);
  * task is booting the system, and such primitives are no-ops).  After this
  * function is called, any synchronous grace-period primitives are run as
  * expedited, with the requesting task driving the grace period forward.
- * A later core_initcall() rcu_exp_runtime_mode() will switch to full
+ * A later core_initcall() rcu_set_runtime_mode() will switch to full
  * runtime RCU functionality.
  */
 void rcu_scheduler_starting(void)

kernel/rcu/tree_exp.h

@@ -737,15 +737,3 @@ void synchronize_rcu_expedited(void)
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
-
-/*
- * Switch to run-time mode once Tree RCU has fully initialized.
- */
-static int __init rcu_exp_runtime_mode(void)
-{
-	rcu_test_sync_prims();
-	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
-	rcu_test_sync_prims();
-	return 0;
-}
-core_initcall(rcu_exp_runtime_mode);

kernel/rcu/update.c

@@ -124,7 +124,7 @@ EXPORT_SYMBOL(rcu_read_lock_sched_held);
  * non-expedited counterparts?  Intended for use within RCU.  Note
  * that if the user specifies both rcu_expedited and rcu_normal, then
  * rcu_normal wins.  (Except during the time period during boot from
- * when the first task is spawned until the rcu_exp_runtime_mode()
+ * when the first task is spawned until the rcu_set_runtime_mode()
  * core_initcall() is invoked, at which point everything is expedited.)
  */
 bool rcu_gp_is_normal(void)
@@ -190,6 +190,39 @@ void rcu_end_inkernel_boot(void)
 
 #endif /* #ifndef CONFIG_TINY_RCU */
 
+/*
+ * Test each non-SRCU synchronous grace-period wait API.  This is
+ * useful just after a change in mode for these primitives, and
+ * during early boot.
+ */
+void rcu_test_sync_prims(void)
+{
+	if (!IS_ENABLED(CONFIG_PROVE_RCU))
+		return;
+	synchronize_rcu();
+	synchronize_rcu_bh();
+	synchronize_sched();
+	synchronize_rcu_expedited();
+	synchronize_rcu_bh_expedited();
+	synchronize_sched_expedited();
+}
+
+#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
+
+/*
+ * Switch to run-time mode once RCU has fully initialized.
+ */
+static int __init rcu_set_runtime_mode(void)
+{
+	rcu_test_sync_prims();
+	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
+	rcu_test_sync_prims();
+	return 0;
+}
+core_initcall(rcu_set_runtime_mode);
+
+#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
+
 #ifdef CONFIG_PREEMPT_RCU
 
 /*
@@ -817,23 +850,6 @@ static void rcu_spawn_tasks_kthread(void)
 
 #endif /* #ifdef CONFIG_TASKS_RCU */
 
-/*
- * Test each non-SRCU synchronous grace-period wait API.  This is
- * useful just after a change in mode for these primitives, and
- * during early boot.
- */
-void rcu_test_sync_prims(void)
-{
-	if (!IS_ENABLED(CONFIG_PROVE_RCU))
-		return;
-	synchronize_rcu();
-	synchronize_rcu_bh();
-	synchronize_sched();
-	synchronize_rcu_expedited();
-	synchronize_rcu_bh_expedited();
-	synchronize_sched_expedited();
-}
-
 #ifdef CONFIG_PROVE_RCU
 
 /*