mtx_owner
td = mtx_owner(m);
td = mtx_owner(m);
owner = mtx_owner(m);
MPASS(owner == mtx_owner(m));
#define mtx_owned(m) (mtx_owner(m) == curthread)
#define ZDOM_OWNED(z) (mtx_owner(&(z)->uzd_lock) != NULL)