Fix reload panic in socket_listener input plugin (#6218)

(cherry picked from commit 60c8f38)

plugins/inputs/socket_listener/socket_listener.go

@@ -37,6 +37,8 @@ type streamSocketListener struct {
 func (ssl *streamSocketListener) listen() {
 	ssl.connections = map[string]net.Conn{}
 
+	wg := sync.WaitGroup{}
+
 	for {
 		c, err := ssl.Accept()
 		if err != nil {
@@ -67,14 +69,20 @@ func (ssl *streamSocketListener) listen() {
 			ssl.AddError(fmt.Errorf("unable to configure keep alive (%s): %s", ssl.ServiceAddress, err))
 		}
 
-		go ssl.read(c)
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			ssl.read(c)
+		}()
 	}
 
 	ssl.connectionsMtx.Lock()
 	for _, c := range ssl.connections {
 		c.Close()
 	}
 	ssl.connectionsMtx.Unlock()
+
+	wg.Wait()
 }
 
 func (ssl *streamSocketListener) setKeepAlive(c net.Conn) error {
@@ -169,6 +177,8 @@ type SocketListener struct {
 	SocketMode      string             `toml:"socket_mode"`
 	tlsint.ServerConfig
 
+	wg sync.WaitGroup
+
 	parsers.Parser
 	telegraf.Accumulator
 	io.Closer
@@ -302,7 +312,12 @@ func (sl *SocketListener) Start(acc telegraf.Accumulator) error {
 		}
 
 		sl.Closer = ssl
-		go ssl.listen()
+		sl.wg = sync.WaitGroup{}
+		sl.wg.Add(1)
+		go func() {
+			defer sl.wg.Done()
+			ssl.listen()
+		}()
 	case "udp", "udp4", "udp6", "ip", "ip4", "ip6", "unixgram":
 		pc, err := udpListen(protocol, addr)
 		if err != nil {
@@ -336,7 +351,12 @@ func (sl *SocketListener) Start(acc telegraf.Accumulator) error {
 		}
 
 		sl.Closer = psl
-		go psl.listen()
+		sl.wg = sync.WaitGroup{}
+		sl.wg.Add(1)
+		go func() {
+			defer sl.wg.Done()
+			psl.listen()
+		}()
 	default:
 		return fmt.Errorf("unknown protocol '%s' in '%s'", protocol, sl.ServiceAddress)
 	}
@@ -378,6 +398,7 @@ func (sl *SocketListener) Stop() {
 		sl.Close()
 		sl.Closer = nil
 	}
+	sl.wg.Wait()
 }
 
 func newSocketListener() *SocketListener {