rcutorture: Dump trace buffer for callback pipe drain failures

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/rcutorture.c

@@ -1060,8 +1060,10 @@ rcu_torture_writer(void *arg)
 			for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++)
 				if (list_empty(&rcu_tortures[i].rtort_free) &&
 				    rcu_access_pointer(rcu_torture_current) !=
-				    &rcu_tortures[i])
+				    &rcu_tortures[i]) {
+					rcu_ftrace_dump(DUMP_ALL);
 					WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count);
+				}
 	} while (!torture_must_stop());
 	/* Reset expediting back to unexpedited. */
 	if (expediting > 0)