rcu: mark rcutorture boosting callback as being on-stack

The CONFIG_DEBUG_OBJECTS_RCU_HEAD facility requires that on-stack RCU
callbacks be flagged explicitly to debug-objects using the
init_rcu_head_on_stack() and destroy_rcu_head_on_stack() functions.
This commit applies those functions to the rcutorture code that tests
RCU priority boosting.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

kernel/rcutorture.c

@@ -749,6 +749,7 @@ static int rcu_torture_boost(void *arg)
 		n_rcu_torture_boost_rterror++;
 	}
 
+	init_rcu_head_on_stack(&rbi.rcu);
 	/* Each pass through the following loop does one boost-test cycle. */
 	do {
 		/* Wait for the next test interval. */
@@ -808,6 +809,7 @@ checkwait:	rcu_stutter_wait("rcu_torture_boost");
 
 	/* Clean up and exit. */
 	VERBOSE_PRINTK_STRING("rcu_torture_boost task stopping");
+	destroy_rcu_head_on_stack(&rbi.rcu);
 	rcutorture_shutdown_absorb("rcu_torture_boost");
 	while (!kthread_should_stop() || rbi.inflight)
 		schedule_timeout_uninterruptible(1);