If a counter event source is disabled while in System.Diagnostics.Tracing.CounterGroup.OnTimer, thread could end up in infinite loop. This happens since _pollingIntervalInMilliseconds is set to 0 when disabled, meaning that we could fail to advance _nextPollingTimeStamp past now:

lock (s_counterGroupLock)
{
    _timeStampSinceCollectionStarted = now;
    do
    {
        _nextPollingTimeStamp += new TimeSpan(0, 0, 0, 0, _pollingIntervalInMilliseconds);
    } while (_nextPollingTimeStamp <= now);
}

Fix use the local copy of pollingIntervalInMilliseconds and also adds an additional safe quard to make sure it always gets advance event if disabled check on _eventSource.IsEnabled() and lock (s_counterGroupLock), since that case will set _pollingIntervalInMilliseconds to 0 as well even before loaded into local variable.