rb_find_first
pos = rb_find_first(&pmu_idx, units, pmu_idx_cmp);
for ((node) = rb_find_first((key), (tree), (cmp)); \
node = rb_find_first(&key, &groups->tree, __group_cmp);
node = rb_find_first(&key, tree, __group_cmp_ignore_cgroup);
node = rb_find_first(&key, tree, __group_cmp_ignore_cgroup);
node = rb_find_first(&key, tree, __group_cmp_ignore_cgroup);
node = rb_find_first((void *)cookie, &rq->core_tree, rb_sched_core_cmp);
for ((node) = rb_find_first((key), (tree), (cmp)); \