ACL_NOT_CACHED
inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED;
cmpxchg(p, ACL_NOT_CACHED, sentinel);
cmpxchg(p, sentinel, ACL_NOT_CACHED);
cmpxchg(p, ACL_NOT_CACHED, sentinel);
cmpxchg(p, sentinel, ACL_NOT_CACHED);
old = xchg(p, ACL_NOT_CACHED);