OFFSET_TO_LOCK
lp = OFFSET_TO_LOCK(lt, list[i].lock);
lockp = OFFSET_TO_LOCK(lt, *lock);
lockp = OFFSET_TO_LOCK(lt, *lock);
lockp = OFFSET_TO_LOCK(lt, lock);
newl = OFFSET_TO_LOCK(lt, newl_off);
lockp = OFFSET_TO_LOCK(lt, lock);