mu.Lock()
		mu.Lock()
	}()
	awaitBlockedGoroutine(t, "sync.Mutex.Lock", "blockMutexDeep", 1)
	mu.Unlock()
}

// goroutineDeep blocks at stack depth n, including the caller until the test is
// finished.
func goroutineDeep(t *testing.T, n int) {
	if n > 1 {
		goroutineDeep(t, n-1)
		return
	}
	wait := make(chan struct{}, 1)
	t.Cleanup(func() {
		wait <- struct{}{}
	})
	<-wait
}