This is xnu-8019. See this file in:
#include <darwintest.h>

#include <stdatomic.h>

#include <unistd.h>
#include <pthread.h>
#include <sys/ulock.h>

#include <os/tsd.h>

#ifndef __TSD_MACH_THREAD_SELF
#define __TSD_MACH_THREAD_SELF 3
#endif

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wbad-function-cast"
__inline static mach_port_name_t
_os_get_self(void)
{
	mach_port_name_t self = (mach_port_name_t)_os_tsd_get_direct(__TSD_MACH_THREAD_SELF);
	return self;
}
#pragma clang diagnostic pop

T_GLOBAL_META(T_META_RUN_CONCURRENTLY(true));

#pragma mark ulock_non_owner_wake

static _Atomic uint32_t test_ulock;

static void *
test_waiter(void *arg __unused)
{
	for (;;) {
		uint32_t test_ulock_owner = atomic_load_explicit(&test_ulock,
		    memory_order_relaxed);
		int rc = __ulock_wait(UL_UNFAIR_LOCK | ULF_NO_ERRNO, &test_ulock,
		    test_ulock_owner, 0);
		if (rc == -EINTR || rc == -EFAULT) {
			continue;
		}
		T_ASSERT_GE(rc, 0, "__ulock_wait");
		break;
	}

	T_PASS("Waiter woke");
	T_END;

	return NULL;
}

static void *
test_waker(void *arg __unused)
{
	for (;;) {
		int rc = __ulock_wake(UL_UNFAIR_LOCK | ULF_NO_ERRNO | ULF_WAKE_ALLOW_NON_OWNER,
		    &test_ulock, 0);
		if (rc == -EINTR) {
			continue;
		}
		T_ASSERT_EQ(rc, 0, "__ulock_wake");
		break;
	}
	return NULL;
}

T_DECL(ulock_non_owner_wake, "ulock_wake respects non-owner wakes",
    T_META_CHECK_LEAKS(false))
{
	pthread_t waiter, waker;

	atomic_store_explicit(&test_ulock, _os_get_self() & ~0x3u, memory_order_relaxed);

	T_ASSERT_POSIX_ZERO(pthread_create(&waiter, NULL, test_waiter, NULL), "create waiter");

	// wait for the waiter to reach the kernel
	for (;;) {
		int kernel_ulocks = __ulock_wake(UL_DEBUG_HASH_DUMP_PID, NULL, 0);
		T_QUIET; T_ASSERT_NE(kernel_ulocks, -1, "UL_DEBUG_HASH_DUMP_PID");

		if (kernel_ulocks == 1) {
			T_LOG("waiter is now waiting");
			break;
		}
		usleep(100);
	}

	T_ASSERT_POSIX_ZERO(pthread_create(&waker, NULL, test_waker, NULL), "create waker");

	// won't ever actually join
	pthread_join(waiter, NULL);
}