Function do_sem2_wake

freebsd/kern/kern_umtx.c:3352–3398

* Signal a userland semaphore. */

 * Signal a userland semaphore.
 */
static int
do_sem2_wake(struct thread *td, struct _usem2 *sem)
{
	struct umtx_key key;
	int error, cnt, rv;
	uint32_t count, flags;

	rv = fueword32(&sem->_flags, &flags);
	if (rv == -1)
		return (EFAULT);
	if ((error = umtx_key_get(sem, TYPE_SEM, GET_SHARE(flags), &key)) != 0)
		return (error);
	umtxq_lock(&key);
	umtxq_busy(&key);
	cnt = umtxq_count(&key);
	if (cnt > 0) {
		/*
		 * If this was the last sleeping thread, clear the waiters
		 * flag in _count.
		 */
		if (cnt == 1) {
			umtxq_unlock(&key);
			rv = fueword32(&sem->_count, &count);
			while (rv != -1 && count & USEM_HAS_WAITERS) {
				rv = casueword32(&sem->_count, count, &count,
				    count & ~USEM_HAS_WAITERS);
				if (rv == 1) {
					rv = thread_check_susp(td, true);
					if (rv != 0)
						break;
				}
			}
			if (rv == -1)
				error = EFAULT;
			else if (rv > 0) {
				error = rv;
			}
			umtxq_lock(&key);
		}

		umtxq_signal(&key, 1);
	}
	umtxq_unbusy(&key);
	umtxq_unlock(&key);
	umtx_key_release(&key);
	return (error);
}

inline int
umtx_copyin_timeout(const void *uaddr, struct timespec *tsp)