- a_inc(&rw->_rw_readers);
- if (rw->_rw_wrlock) {
- a_dec(&rw->_rw_readers);
- if (rw->_rw_waiters && !rw->_rw_readers)
- __wake(&rw->_rw_readers, 1, 0);
- return EAGAIN;
- }
+ int val, cnt;
+ do {
+ val = rw->_rw_lock;
+ cnt = val & 0x7fffffff;
+ if (cnt == 0x7fffffff) return EBUSY;
+ if (cnt == 0x7ffffffe) return EAGAIN;
+ } while (a_cas(&rw->_rw_lock, val, val+1) != val);