Function do_lock_pi

freebsd/kern/kern_umtx.c:1793–1991

* Lock a PI mutex. */

 * Lock a PI mutex.
 */
static int
do_lock_pi(struct thread *td, struct umutex *m, uint32_t flags,
    struct _umtx_time *timeout, int try)
{
	struct abs_timeout timo;
	struct umtx_q *uq;
	struct umtx_pi *pi, *new_pi;
	uint32_t id, old_owner, owner, old;
	int error, rv;

	id = td->td_tid;
	uq = td->td_umtxq;

	if ((error = umtx_key_get(m, (flags & UMUTEX_ROBUST) != 0 ?
	    TYPE_PI_ROBUST_UMUTEX : TYPE_PI_UMUTEX, GET_SHARE(flags),
	    &uq->uq_key)) != 0)
		return (error);

	if (timeout != NULL)
		abs_timeout_init2(&timo, timeout);

	umtxq_lock(&uq->uq_key);
	pi = umtx_pi_lookup(&uq->uq_key);
	if (pi == NULL) {
		new_pi = umtx_pi_alloc(M_NOWAIT);
		if (new_pi == NULL) {
			umtxq_unlock(&uq->uq_key);
			new_pi = umtx_pi_alloc(M_WAITOK);
			umtxq_lock(&uq->uq_key);
			pi = umtx_pi_lookup(&uq->uq_key);
			if (pi != NULL) {
				umtx_pi_free(new_pi);
				new_pi = NULL;
			}
		}
		if (new_pi != NULL) {
			new_pi->pi_key = uq->uq_key;
			umtx_pi_insert(new_pi);
			pi = new_pi;
		}
	}
	umtx_pi_ref(pi);
	umtxq_unlock(&uq->uq_key);

	/*
	 * Care must be exercised when dealing with umtx structure.  It
	 * can fault on any access.
	 */
	for (;;) {
		/*
		 * Try the uncontested case.  This should be done in userland.
		 */
		rv = casueword32(&m->m_owner, UMUTEX_UNOWNED, &owner, id);
		/* The address was invalid. */
		if (rv == -1) {
			error = EFAULT;
			break;
		}