Function do_unlock_normal

freebsd/kern/kern_umtx.c:1162–1231

* Unlock PTHREAD_PRIO_NONE protocol POSIX mutex. */

 * Unlock PTHREAD_PRIO_NONE protocol POSIX mutex.
 */
static int
do_unlock_normal(struct thread *td, struct umutex *m, uint32_t flags, bool rb)
{
	struct umtx_key key;
	uint32_t owner, old, id, newlock;
	int error, count;

	id = td->td_tid;

again:
	/*
	 * Make sure we own this mtx.
	 */
	error = fueword32(&m->m_owner, &owner);
	if (error == -1)
		return (EFAULT);

	if ((owner & ~UMUTEX_CONTESTED) != id)
		return (EPERM);

	newlock = umtx_unlock_val(flags, rb);
	if ((owner & UMUTEX_CONTESTED) == 0) {
		error = casueword32(&m->m_owner, owner, &old, newlock);
		if (error == -1)
			return (EFAULT);
		if (error == 1) {
			error = thread_check_susp(td, false);
			if (error != 0)
				return (error);
			goto again;
		}
		MPASS(old == owner);
		return (0);
	}

	/* We should only ever be in here for contested locks */
	if ((error = umtx_key_get(m, TYPE_NORMAL_UMUTEX, GET_SHARE(flags),
	    &key)) != 0)
		return (error);

	umtxq_lock(&key);
	umtxq_busy(&key);
	count = umtxq_count(&key);
	umtxq_unlock(&key);

	/*
	 * When unlocking the umtx, it must be marked as unowned if
	 * there is zero or one thread only waiting for it.
	 * Otherwise, it must be marked as contested.
	 */
	if (count > 1)
		newlock |= UMUTEX_CONTESTED;
	error = casueword32(&m->m_owner, owner, &old, newlock);
	umtxq_lock(&key);
	umtxq_signal(&key, 1);
	umtxq_unbusy(&key);
	umtxq_unlock(&key);
	umtx_key_release(&key);