rcutorture: Complain when invalid SRCU reader_flavor is specified

Currently, rcutorture ignores reader_flavor bits that are not in the
SRCU_READ_FLAVOR_ALL bitmask, which could confuse rcutorture users into
believing buggy patches had been fully tested.  This commit therefore
produces a splat in this case.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

kernel/rcu/rcutorture.c

@@ -689,6 +689,8 @@ static int srcu_torture_read_lock(void)
 	int idx;
 	int ret = 0;
 
+	WARN_ON_ONCE(reader_flavor & ~SRCU_READ_FLAVOR_ALL);
+
 	if ((reader_flavor & SRCU_READ_FLAVOR_NORMAL) || !(reader_flavor & SRCU_READ_FLAVOR_ALL)) {
 		idx = srcu_read_lock(srcu_ctlp);
 		WARN_ON_ONCE(idx & ~0x1);