worker: fix panic in handle task

dm/worker/server_test.go

@@ -132,6 +132,7 @@ func (t *testServer) TestServer(c *C) {
 
 	// test worker, just make sure testing sort
 	t.testWorker(c)
+	t.testWorkerHandleTask(c)
 }
 
 func (t *testServer) testHTTPInterface(c *C, uri string) {

dm/worker/worker.go

@@ -22,6 +22,7 @@ import (
 	"time"
 
 	"github.com/pingcap/errors"
+	"github.com/pingcap/failpoint"
 	"github.com/siddontang/go/sync2"
 	"github.com/syndtr/goleveldb/leveldb"
 	"go.uber.org/zap"
@@ -707,7 +708,14 @@ func (w *Worker) restoreSubTask() error {
 var maxRetryCount = 10
 
 func (w *Worker) handleTask() {
-	ticker := time.NewTicker(time.Second)
+	var handleTaskInterval = time.Second
+	failpoint.Inject("handleTaskInternal", func(val failpoint.Value) {
+		if milliseconds, ok := val.(int); ok {
+			handleTaskInterval = time.Duration(milliseconds) * time.Millisecond
+			w.l.Info("set handleTaskInterval", zap.String("failpoint", "handleTaskInternal"), zap.Int("value", milliseconds))
+		}
+	})
+	ticker := time.NewTicker(handleTaskInterval)
 	defer ticker.Stop()
 
 	retryCnt := 0
@@ -826,7 +834,11 @@ Loop:
 			// fill current task config
 			if len(opLog.Task.Task) == 0 {
 				tm := w.meta.GetTask(opLog.Task.Name)
-				opLog.Task.Task = append([]byte{}, tm.Task...)
+				if tm == nil {
+					w.l.Warn("task meta not found", zap.String("task", opLog.Task.Name))
+				} else {
+					opLog.Task.Task = append([]byte{}, tm.Task...)
+				}
 			}
 
 			err = w.meta.MarkOperation(opLog)

dm/worker/worker_test.go

@@ -14,10 +14,15 @@
 package worker
 
 import (
+	"sync"
+	"time"
+
 	. "github.com/pingcap/check"
+	"github.com/pingcap/failpoint"
 
 	"github.com/pingcap/dm/dm/config"
 	"github.com/pingcap/dm/dm/pb"
+	"github.com/pingcap/dm/pkg/utils"
 )
 
 var emptyWorkerStatusInfoJSONLength = 25
@@ -65,3 +70,47 @@ func (t *testServer) testWorker(c *C) {
 	_, err = w.OperateSubTask("testSubTask", pb.TaskOp_Stop)
 	c.Assert(err, ErrorMatches, "worker already closed.*")
 }
+
+func (t *testServer) testWorkerHandleTask(c *C) {
+	var (
+		wg       sync.WaitGroup
+		taskName = "test"
+	)
+
+	NewRelayHolder = NewDummyRelayHolder
+	dir := c.MkDir()
+	cfg := NewConfig()
+	c.Assert(cfg.Parse([]string{"-config=./dm-worker.toml"}), IsNil)
+	cfg.RelayDir = dir
+	cfg.MetaDir = dir
+	w, err := NewWorker(cfg)
+	c.Assert(err, IsNil)
+
+	tasks := []*pb.TaskMeta{
+		{Op: pb.TaskOp_Stop, Name: taskName, Stage: pb.Stage_New},
+		{Op: pb.TaskOp_Pause, Name: taskName, Stage: pb.Stage_New},
+		{Op: pb.TaskOp_Resume, Name: taskName, Stage: pb.Stage_New},
+	}
+	for _, task := range tasks {
+		_, err := w.meta.AppendOperation(task)
+		c.Assert(err, IsNil)
+	}
+	c.Assert(len(w.meta.logs), Equals, len(tasks))
+
+	c.Assert(failpoint.Enable("github.com/pingcap/dm/dm/worker/handleTaskInternal", `return(10)`), IsNil)
+	defer failpoint.Disable("github.com/pingcap/dm/dm/worker/handleTaskInternal")
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		w.handleTask()
+	}()
+
+	c.Assert(utils.WaitSomething(5, 10*time.Millisecond, func() bool {
+		w.meta.Lock()
+		defer w.meta.Unlock()
+		return len(w.meta.logs) == 0
+	}), IsTrue)
+
+	w.Close()
+	wg.Wait()
+}