server: fix connection close on network timeout/read error (#34757) (#…

…35498)

close #34722

server/conn.go

@@ -311,8 +311,16 @@ func (cc *clientConn) Close() error {
 
 func closeConn(cc *clientConn, connections int) error {
 	metrics.ConnGauge.Set(float64(connections))
-	err := cc.bufReadConn.Close()
-	terror.Log(err)
+	if cc.bufReadConn != nil {
+		err := cc.bufReadConn.Close()
+		if err != nil {
+			// We need to expect connection might have already disconnected.
+			// This is because closeConn() might be called after a connection read-timeout.
+			logutil.Logger(context.Background()).Debug("could not close connection", zap.Error(err))
+		}
+	}
+	// Close statements and session
+	// This will release advisory locks, row locks, etc.
 	if cc.ctx != nil {
 		return cc.ctx.Close()
 	}
@@ -1021,10 +1029,6 @@ func (cc *clientConn) Run(ctx context.Context) {
 			terror.Log(err)
 			metrics.PanicCounter.WithLabelValues(metrics.LabelSession).Inc()
 		}
-		if atomic.LoadInt32(&cc.status) != connStatusShutdown {
-			err := cc.Close()
-			terror.Log(err)
-		}
 	}()
 
 	// Usually, client connection status changes between [dispatching] <=> [reading].

server/server.go

@@ -525,6 +525,7 @@ func (s *Server) onConn(conn *clientConn) {
 	logutil.Logger(ctx).Debug("new connection", zap.String("remoteAddr", conn.bufReadConn.RemoteAddr().String()))
 
 	defer func() {
+		terror.Log(conn.Close())
 		logutil.Logger(ctx).Debug("connection closed")
 	}()
 	s.rwlock.Lock()