diff --git a/core/server/udp.go b/core/server/udp.go
index 0ec0d5e..3d7cd71 100644
--- a/core/server/udp.go
+++ b/core/server/udp.go
@@ -40,9 +40,6 @@ type udpSessionEntry struct {
 	DialFunc func(addr string, firstMsgData []byte) (conn UDPConn, actualAddr string, err error)
 	ExitFunc func(err error)
 
-	timeoutChan chan struct{}
-	exitChan    chan error
-
 	conn     UDPConn
 	connLock sync.Mutex
 	closed   bool
@@ -61,34 +58,30 @@ func newUDPSessionEntry(
 
 		DialFunc: dialFunc,
 		ExitFunc: exitFunc,
-
-		timeoutChan: make(chan struct{}),
-		exitChan:    make(chan error, 2),
 	}
 
-	go func() {
-		// Guard routine
-		var err error
-		select {
-		case <-e.timeoutChan:
-			// Use nil error to indicate timeout.
-		case err = <-e.exitChan:
-		}
-
-		// We need this lock to ensure not to create conn after session exit
-		e.connLock.Lock()
-		e.closed = true
-		if e.conn != nil {
-			_ = e.conn.Close()
-		}
-		e.connLock.Unlock()
-
-		e.ExitFunc(err)
-	}()
-
 	return
 }
 
+func (e *udpSessionEntry) CloseWithErr(err error) {
+	// We need this lock to ensure not to create conn after session exit
+	e.connLock.Lock()
+
+	if e.closed {
+		// Already closed
+		e.connLock.Unlock()
+		return
+	}
+
+	e.closed = true
+	if e.conn != nil {
+		_ = e.conn.Close()
+	}
+	e.connLock.Unlock()
+
+	e.ExitFunc(err)
+}
+
 // Feed feeds a UDP message to the session.
 // If the message itself is a complete message, or it completes a fragmented message,
 // the message is written to the session's UDP connection, and the number of bytes
@@ -121,17 +114,18 @@ func (e *udpSessionEntry) Feed(msg *protocol.UDPMessage) (int, error) {
 func (e *udpSessionEntry) initConn(firstMsg *protocol.UDPMessage) error {
 	// We need this lock to ensure not to create conn after session exit
 	e.connLock.Lock()
-	defer e.connLock.Unlock()
 
 	if e.closed {
+		e.connLock.Unlock()
 		return errors.New("session is closed")
 	}
 
 	conn, actualAddr, err := e.DialFunc(firstMsg.Addr, firstMsg.Data)
 	if err != nil {
-		// Fail fast if DailFunc failed
+		// Fail fast if DialFunc failed
 		// (usually indicates the connection has been rejected by the ACL)
-		e.exitChan <- err
+		e.connLock.Unlock()
+		e.CloseWithErr(err)
 		return err
 	}
 
@@ -141,6 +135,8 @@ func (e *udpSessionEntry) initConn(firstMsg *protocol.UDPMessage) error {
 		e.OriginalAddr = firstMsg.Addr
 	}
 	go e.receiveLoop()
+
+	e.connLock.Unlock()
 	return nil
 }
 
@@ -154,7 +150,7 @@ func (e *udpSessionEntry) receiveLoop() {
 	for {
 		udpN, rAddr, err := e.conn.ReadFrom(udpBuf)
 		if err != nil {
-			e.exitChan <- err
+			e.CloseWithErr(err)
 			return
 		}
 		e.Last.Set(time.Now())
@@ -176,7 +172,7 @@ func (e *udpSessionEntry) receiveLoop() {
 		}
 		err = sendMessageAutoFrag(e.IO, msgBuf, msg)
 		if err != nil {
-			e.exitChan <- err
+			e.CloseWithErr(err)
 			return
 		}
 	}
@@ -185,10 +181,8 @@ func (e *udpSessionEntry) receiveLoop() {
 // MarkTimeout marks the session to be cleaned up due to timeout.
 // Should only be called by the cleanup routine of the session manager.
 func (e *udpSessionEntry) MarkTimeout() {
-	select {
-	case e.timeoutChan <- struct{}{}:
-	default:
-	}
+	// nil error indicates timeout.
+	e.CloseWithErr(nil)
 }
 
 // sendMessageAutoFrag tries to send a UDP message as a whole first,