rcutorture: Enable RCU priority boosting for TREE09

The TREE09 rcutorture scenario exhausts memory from time to time, and
this is due to a reader being preempted and blocking grace periods,
thus preventing recycling of the memory used in callback-flooding tests.
This commit therefore enables RCU priority boosting and sets the boosting
delay to 100 milliseconds after grace-period start.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

tools/testing/selftests/rcutorture/configs/rcu/TREE09

@@ -10,8 +10,9 @@ CONFIG_NO_HZ_FULL=n
 CONFIG_RCU_TRACE=n
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_BOOST=n
+CONFIG_RCU_BOOST=y
+CONFIG_RCU_BOOST_DELAY=100
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
-#CHECK#CONFIG_RCU_EXPERT=n
+CONFIG_RCU_EXPERT=y
 CONFIG_KPROBES=n
 CONFIG_FTRACE=n