refscale: Allow refscale without RCU Tasks

Currently, a CONFIG_PREEMPT_NONE=y kernel substitutes normal RCU for
RCU Tasks.  Unless that kernel builds refscale, whether built-in or as a
module, in which case RCU Tasks is (unnecessarily) built in.  This both
increases kernel size and increases the complexity of certain tracing
operations.  This commit therefore decouples the presence of refscale
from the presence of RCU Tasks.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/Kconfig.debug

@@ -63,7 +63,6 @@ config RCU_REF_SCALE_TEST
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
 	select SRCU
-	select TASKS_RCU
 	select TASKS_RUDE_RCU
 	select TASKS_TRACE_RCU
 	default n

kernel/rcu/refscale.c

@@ -207,6 +207,8 @@ static struct ref_scale_ops srcu_ops = {
 	.name		= "srcu"
 };
 
+#ifdef CONFIG_TASKS_RCU
+
 // Definitions for RCU Tasks ref scale testing: Empty read markers.
 // These definitions also work for RCU Rude readers.
 static void rcu_tasks_ref_scale_read_section(const int nloops)
@@ -232,6 +234,14 @@ static struct ref_scale_ops rcu_tasks_ops = {
 	.name		= "rcu-tasks"
 };
 
+#define RCU_TASKS_OPS &rcu_tasks_ops,
+
+#else // #ifdef CONFIG_TASKS_RCU
+
+#define RCU_TASKS_OPS
+
+#endif // #else // #ifdef CONFIG_TASKS_RCU
+
 // Definitions for RCU Tasks Trace ref scale testing.
 static void rcu_trace_ref_scale_read_section(const int nloops)
 {
@@ -790,7 +800,7 @@ ref_scale_init(void)
 	long i;
 	int firsterr = 0;
 	static struct ref_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &rcu_trace_ops, &rcu_tasks_ops, &refcnt_ops, &rwlock_ops,
+		&rcu_ops, &srcu_ops, &rcu_trace_ops, RCU_TASKS_OPS &refcnt_ops, &rwlock_ops,
 		&rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops,
 	};
 

tools/testing/selftests/rcutorture/configs/refscale/CFcommon

@@ -1,2 +1,4 @@
 CONFIG_RCU_REF_SCALE_TEST=y
 CONFIG_PRINTK_TIME=y
+CONFIG_FORCE_TASKS_RCU=y
+#CHECK#CONFIG_TASKS_RCU=y

tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT

@@ -15,3 +15,5 @@ CONFIG_PROVE_LOCKING=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
+CONFIG_KPROBES=n
+CONFIG_FTRACE=n