[PATCH rcu 1/4] rcu: Create NEED_TASKS_RCU to factor out enablement logic

[Paul E. McKenney]

Currently, if a Kconfig option depends on TASKS_RCU, it conditionally does
"select TASKS_RCU if PREEMPTION".  This works, but requires any change in
this enablement logic to be replicated across all such "select" clauses.
This commit therefore creates a new NEED_TASKS_RCU Kconfig option so
that the default value of TASKS_RCU can depend on a combination of this
new option and any needed enablement logic, so that this logic is in
one place.

While in the area, also anticipate a likely future change by adding
PREEMPT_AUTO to that logic.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/rcu/Kconfig | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 7dca0138260c3..3e079de0f5b43 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -85,9 +85,13 @@ config FORCE_TASKS_RCU
 	  idle, and user-mode execution as quiescent states.  Not for
 	  manual selection in most cases.
 
-config TASKS_RCU
+config NEED_TASKS_RCU
 	bool
 	default n
+
+config TASKS_RCU
+	bool
+	default NEED_TASKS_RCU && (PREEMPTION || PREEMPT_AUTO)
 	select IRQ_WORK
 
 config FORCE_TASKS_RUDE_RCU
-- 
2.40.1