rcutorture: Test rcu_tasks_trace_expedite_current()

This commit adds a ->exp_current member to the tasks_tracing_ops structure
to test the rcu_tasks_trace_expedite_current() function.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

kernel/rcu/rcutorture.c

@@ -1178,6 +1178,7 @@ static struct rcu_torture_ops tasks_tracing_ops = {
 	.deferred_free	= rcu_tasks_tracing_torture_deferred_free,
 	.sync		= synchronize_rcu_tasks_trace,
 	.exp_sync	= synchronize_rcu_tasks_trace,
+	.exp_current	= rcu_tasks_trace_expedite_current,
 	.call		= call_rcu_tasks_trace,
 	.cb_barrier	= rcu_barrier_tasks_trace,
 	.cbflood_max	= 50000,