CLONE_CHILD_CLEARTID
p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? args->child_tid : NULL;
if (!(flags & (CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID)))
CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID |
CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID |