MPL_UNLOCKED
if (old_lock == MPL_UNLOCKED) {
*lock = MPL_UNLOCKED;
lock->mpl_lock[0] = MPL_UNLOCKED;
lock->mpl_lock[1] = MPL_UNLOCKED;
lock->mpl_lock[2] = MPL_UNLOCKED;
lock->mpl_lock[3] = MPL_UNLOCKED;