rcutorture: Add RCU-tasks qualifier to dereference

Although RCU-tasks isn't really designed to support rcu_dereference()
and list manipulation, that is how rcutorture tests it.  Which means
that lockdep-RCU complains about the rcu_dereference_check() invocations
because RCU-tasks doesn't have read-side markers.  This commit therefore
creates a torturing_tasks() to silence the lockdep-RCU complaints from
rcu_dereference_check() when RCU-tasks is being tortured.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/rcutorture.c

@@ -684,10 +684,20 @@ static struct rcu_torture_ops tasks_ops = {
 
 #define RCUTORTURE_TASKS_OPS &tasks_ops,
 
+static bool __maybe_unused torturing_tasks(void)
+{
+	return cur_ops == &tasks_ops;
+}
+
 #else /* #ifdef CONFIG_TASKS_RCU */
 
 #define RCUTORTURE_TASKS_OPS
 
+static bool torturing_tasks(void)
+{
+	return false;
+}
+
 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 
 /*
@@ -1087,7 +1097,8 @@ static void rcu_torture_timer(unsigned long unused)
 	p = rcu_dereference_check(rcu_torture_current,
 				  rcu_read_lock_bh_held() ||
 				  rcu_read_lock_sched_held() ||
-				  srcu_read_lock_held(srcu_ctlp));
+				  srcu_read_lock_held(srcu_ctlp) ||
+				  torturing_tasks());
 	if (p == NULL) {
 		/* Leave because rcu_torture_writer is not yet underway */
 		cur_ops->readunlock(idx);
@@ -1161,7 +1172,8 @@ rcu_torture_reader(void *arg)
 		p = rcu_dereference_check(rcu_torture_current,
 					  rcu_read_lock_bh_held() ||
 					  rcu_read_lock_sched_held() ||
-					  srcu_read_lock_held(srcu_ctlp));
+					  srcu_read_lock_held(srcu_ctlp) ||
+					  torturing_tasks());
 		if (p == NULL) {
 			/* Wait for rcu_torture_writer to get underway */
 			cur_ops->readunlock(idx);