diff --git a/worker/cgroup.go b/worker/cgroup.go
index 097aaa7..26ae7e9 100644
--- a/worker/cgroup.go
+++ b/worker/cgroup.go
@@ -2,18 +2,20 @@ package worker
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
 	"strconv"
 	"syscall"
+	"time"
 
 	"golang.org/x/sys/unix"
 
 	"github.com/codeskyblue/go-sh"
 )
 
-var cgSubsystem string = "cpu"
+var cgSubsystem = "cpu"
 
 type cgroupHook struct {
 	emptyHook
@@ -82,23 +84,43 @@ func (c *cgroupHook) killAll() error {
 		return nil
 	}
 	name := c.provider.Name()
-	taskFile, err := os.Open(filepath.Join(c.basePath, cgSubsystem, c.baseGroup, name, "tasks"))
-	if err != nil {
-		return err
+
+	readTaskList := func() ([]int, error) {
+		taskList := []int{}
+		taskFile, err := os.Open(filepath.Join(c.basePath, cgSubsystem, c.baseGroup, name, "tasks"))
+		if err != nil {
+			return taskList, err
+		}
+		defer taskFile.Close()
+
+		scanner := bufio.NewScanner(taskFile)
+		for scanner.Scan() {
+			pid, err := strconv.Atoi(scanner.Text())
+			if err != nil {
+				return taskList, err
+			}
+			taskList = append(taskList, pid)
+		}
+		return taskList, nil
 	}
-	defer taskFile.Close()
-	taskList := []int{}
-	scanner := bufio.NewScanner(taskFile)
-	for scanner.Scan() {
-		pid, err := strconv.Atoi(scanner.Text())
+
+	for i := 0; i < 4; i++ {
+		if i == 3 {
+			return errors.New("Unable to kill all child tasks")
+		}
+		taskList, err := readTaskList()
 		if err != nil {
 			return err
 		}
-		taskList = append(taskList, pid)
-	}
-	for _, pid := range taskList {
-		logger.Debugf("Killing process: %d", pid)
-		unix.Kill(pid, syscall.SIGKILL)
+		if len(taskList) == 0 {
+			return nil
+		}
+		for _, pid := range taskList {
+			logger.Debugf("Killing process: %d", pid)
+			unix.Kill(pid, syscall.SIGKILL)
+		}
+		// sleep 10ms for the first round, and 1.01s, 2.01s, 3.01s for the rest
+		time.Sleep(time.Duration(i)*time.Second + 10*time.Millisecond)
 	}
 
 	return nil