Set the recursion available flag

go mod tidy

internal/dns/dns.go

@@ -172,6 +172,8 @@ func (m measurement) String() string {
 }
 
 func (s *Server) probeUpstreamLatency() {
+	if !s.once {
+		s.once = true
 		upstreams := s.upstreams()
 		results := make([]measurement, len(upstreams))
 		var wg sync.WaitGroup
@@ -199,7 +201,7 @@ func (s *Server) probeUpstreamLatency() {
 		sort.Slice(results, func(i, j int) bool {
 			return results[i].rtt < results[j].rtt
 		})
-	log.Printf("probe results: %v", results)
+		log.Printf("probe results: %v %v", s.once, results)
 		for idx, result := range results {
 			upstreams[idx] = result.upstream
 		}
@@ -207,6 +209,7 @@ func (s *Server) probeUpstreamLatency() {
 		defer s.upstreamMu.Unlock()
 		s.upstream = upstreams
 	}
+}
 
 func (s *Server) hostByName(n lcHostname) (string, bool) {
 	s.mu.Lock()