MTX_LOCK
: "r"(MTX_LOCK), "r"(__mtx));
return (__old & MTX_LOCK) == 0;
:: "r"(~MTX_LOCK), "r"(__mtx));
__mtx->mtx_owner &= ~MTX_LOCK;
return (__mtx->mtx_owner & MTX_LOCK) != 0;