Function do_unlock_pp

freebsd/kern/kern_umtx.c:2295–2376

* Unlock a PP mutex. */

 * Unlock a PP mutex.
 */
static int
do_unlock_pp(struct thread *td, struct umutex *m, uint32_t flags, bool rb)
{
	struct umtx_key key;
	struct umtx_q *uq, *uq2;
	struct umtx_pi *pi;
	uint32_t id, owner, rceiling;
	int error, pri, new_inherited_pri, su;

	id = td->td_tid;
	uq = td->td_umtxq;
	su = (priv_check(td, PRIV_SCHED_RTPRIO) == 0);

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

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

	error = copyin(&m->m_ceilings[1], &rceiling, sizeof(uint32_t));
	if (error != 0)
		return (error);

	if (rceiling == -1)
		new_inherited_pri = PRI_MAX;
	else {
		rceiling = RTP_PRIO_MAX - rceiling;
		if (rceiling > RTP_PRIO_MAX)
			return (EINVAL);
		new_inherited_pri = PRI_MIN_REALTIME + rceiling;
	}

	if ((error = umtx_key_get(m, (flags & UMUTEX_ROBUST) != 0 ?
	    TYPE_PP_ROBUST_UMUTEX : TYPE_PP_UMUTEX, GET_SHARE(flags),
	    &key)) != 0)
		return (error);
	umtxq_lock(&key);
	umtxq_busy(&key);
	umtxq_unlock(&key);
	/*
	 * For priority protected mutex, always set unlocked state
	 * to UMUTEX_CONTESTED, so that userland always enters kernel
	 * to lock the mutex, it is necessary because thread priority
	 * has to be adjusted for such mutex.
	 */
	error = suword32(&m->m_owner, umtx_unlock_val(flags, rb) |
	    UMUTEX_CONTESTED);

	umtxq_lock(&key);
	if (error == 0)
		umtxq_signal(&key, 1);
	umtxq_unbusy(&key);
	umtxq_unlock(&key);