Protect devfs last ruleset acquiring with mutex

cmd/root.go

@@ -1,11 +1,12 @@
 package cmd
 
 import (
-	"encoding/json"
-	"fmt"
-	"io/ioutil"
 	"os"
+	"fmt"
+	"sync"
 	"strings"
+	"io/ioutil"
+	"encoding/json"
 
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
@@ -55,6 +56,7 @@ var (
 	gFetchIntoDS     string
 	gFetchFrom       string
 
+	gMdevfs          sync.Mutex
 
 	rootCmd = &cobra.Command{
 		Use:   "gocage",