Mutex vs RWMutex and data races?

Question

I'm pretty new in Go and need the answers to some of dilemmas while implementing small HTTP notifier than runs concurrently, sending message to the configured HTTP endpoint. For that purpose, I use the following structure:

type Notifier struct {
    url          string
    waitingQueue *list.List
    progress   *list.List

    errs chan NotificationError

    active sync.WaitGroup
    mu     sync.Mutex
}

Here is the notify method:

func (hn *Notifier) Notify(message string) {
    if hn.ProcessingCount() < hn.config.MaxActiveRequestsCount() && hn.checkIfOlderThanOldestWaiting(time.Now().Unix()) {
        element := hn.addToProgressQueue(message)
        hn.active.Add(1)
        go hn.sendNotification(element)
    } else {
        hn.waitingQueue.PushBack(QueueItem{message, time.Now().UnixNano()})
    }
}

And addToInProgressQueue:

func (hn *Notifier) addToProgressQueue(message string) *list.Element {
    hn.mu.Lock()
    defer hn.mu.Unlock()

    queueItem := QueueItem{message, time.Now().UnixNano()}
    element := hn.progress.PushBack(queueItem)
    return element
}

1. I guess this won't work as expected for concurrent reads/writes of queue? Is it enought to use RWMutex instead of Mutex to ensure the locks are working properly?

2. The code of ProcessingCount

func (hn *Notifier) ProcessingCount() int {
    hn.mu.Lock()
    defer hn.mu.Unlock()

    return hn.inProgress.Len()
}

Can there be a data race here?

Also, if you have some good resources on data race examples in Golang, it would be well appreciated.

Thanks in advance