rcu-tasks: Allow standalone use of TASKS_{TRACE_,}RCU

This commit allows TASKS_TRACE_RCU to be used independently of TASKS_RCU
and vice versa.

[ paulmck: Fix conditional compilation per kbuild test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tasks.h

@@ -244,27 +244,6 @@ static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp)
 	smp_mb(); /* Ensure others see full kthread. */
 }
 
-/* Do the srcu_read_lock() for the above synchronize_srcu().  */
-void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
-{
-	preempt_disable();
-	current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
-	preempt_enable();
-}
-
-static void exit_tasks_rcu_finish_trace(struct task_struct *t);
-
-/* Do the srcu_read_unlock() for the above synchronize_srcu().  */
-void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
-{
-	struct task_struct *t = current;
-
-	preempt_disable();
-	__srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
-	preempt_enable();
-	exit_tasks_rcu_finish_trace(t);
-}
-
 #ifndef CONFIG_TINY_RCU
 
 /*
@@ -303,7 +282,9 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
 		s);
 }
 
-#ifdef CONFIG_TASKS_RCU
+static void exit_tasks_rcu_finish_trace(struct task_struct *t);
+
+#if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU)
 
 ////////////////////////////////////////////////////////////////////////
 //
@@ -374,6 +355,10 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
 	rtp->postgp_func(rtp);
 }
 
+#endif /* #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) */
+
+#ifdef CONFIG_TASKS_RCU
+
 ////////////////////////////////////////////////////////////////////////
 //
 // Simple variant of RCU whose quiescent states are voluntary context
@@ -577,8 +562,29 @@ static void show_rcu_tasks_classic_gp_kthread(void)
 	show_rcu_tasks_generic_gp_kthread(&rcu_tasks, "");
 }
 
+/* Do the srcu_read_lock() for the above synchronize_srcu().  */
+void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
+{
+	preempt_disable();
+	current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
+	preempt_enable();
+}
+
+/* Do the srcu_read_unlock() for the above synchronize_srcu().  */
+void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
+{
+	struct task_struct *t = current;
+
+	preempt_disable();
+	__srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
+	preempt_enable();
+	exit_tasks_rcu_finish_trace(t);
+}
+
 #else /* #ifdef CONFIG_TASKS_RCU */
 static void show_rcu_tasks_classic_gp_kthread(void) { }
+void exit_tasks_rcu_start(void) { }
+void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); }
 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 
 #ifdef CONFIG_TASKS_RUDE_RCU
@@ -1075,7 +1081,7 @@ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp)
 }
 
 /* Report any needed quiescent state for this exiting task. */
-void exit_tasks_rcu_finish_trace(struct task_struct *t)
+static void exit_tasks_rcu_finish_trace(struct task_struct *t)
 {
 	WRITE_ONCE(t->trc_reader_checked, true);
 	WARN_ON_ONCE(t->trc_reader_nesting);
@@ -1170,7 +1176,7 @@ static void show_rcu_tasks_trace_gp_kthread(void)
 }
 
 #else /* #ifdef CONFIG_TASKS_TRACE_RCU */
-void exit_tasks_rcu_finish_trace(struct task_struct *t) { }
+static void exit_tasks_rcu_finish_trace(struct task_struct *t) { }
 static inline void show_rcu_tasks_trace_gp_kthread(void) {}
 #endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */