br: fix checkpoint cannot advance after pause->stop->start

br/pkg/streamhelper/BUILD.bazel

@@ -69,7 +69,7 @@ go_test(
     ],
     flaky = True,
     race = "on",
-    shard_count = 27,
+    shard_count = 28,
     deps = [
         ":streamhelper",
         "//br/pkg/errors",

br/pkg/streamhelper/advancer.go

@@ -434,6 +434,7 @@ func (c *CheckpointAdvancer) onTaskEvent(ctx context.Context, e TaskEvent) error
 	case EventDel:
 		utils.LogBackupTaskCountDec()
 		c.task = nil
+		c.isPaused.Store(false)
 		c.taskRange = nil
 		// This would be synced by `taskMu`, perhaps we'd better rename that to `tickMu`.
 		// Do the null check because some of test cases won't equip the advancer with subscriber.
@@ -450,11 +451,11 @@ func (c *CheckpointAdvancer) onTaskEvent(ctx context.Context, e TaskEvent) error
 		metrics.LastCheckpoint.DeleteLabelValues(e.Name)
 	case EventPause:
 		if c.task.GetName() == e.Name {
-			c.isPaused.CompareAndSwap(false, true)
+			c.isPaused.Store(true)
 		}
 	case EventResume:
 		if c.task.GetName() == e.Name {
-			c.isPaused.CompareAndSwap(true, false)
+			c.isPaused.Store(false)
 		}
 	case EventErr:
 		return e.Err

br/pkg/streamhelper/advancer_test.go

@@ -541,6 +541,33 @@ func TestCheckPointResume(t *testing.T) {
 	require.ErrorContains(t, adv.OnTick(ctx), "lagged too large")
 }
 
+func TestUnregisterAfterPause(t *testing.T) {
+	c := createFakeCluster(t, 4, false)
+	defer func() {
+		fmt.Println(c)
+	}()
+	c.splitAndScatter("01", "02", "022", "023", "033", "04", "043")
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	env := &testEnv{fakeCluster: c, testCtx: t}
+	adv := streamhelper.NewCheckpointAdvancer(env)
+	adv.UpdateConfigWith(func(c *config.Config) {
+		c.CheckPointLagLimit = 1 * time.Minute
+	})
+	adv.StartTaskListener(ctx)
+	c.advanceClusterTimeBy(1 * time.Minute)
+	require.NoError(t, adv.OnTick(ctx))
+	env.PauseTask(ctx, "whole")
+	time.Sleep(1 * time.Second)
+	c.advanceClusterTimeBy(1 * time.Minute)
+	require.NoError(t, adv.OnTick(ctx))
+	env.unregisterTask()
+	env.putTask()
+	require.Eventually(t, func() bool {
+		return assert.ErrorContains(t, adv.OnTick(ctx), "check point lagged too large")
+	}, 5*time.Second, 300*time.Millisecond)
+}
+
 func TestOwnershipLost(t *testing.T) {
 	c := createFakeCluster(t, 4, false)
 	c.splitAndScatter(manyRegions(0, 10240)...)

br/pkg/streamhelper/basic_lib_for_test.go

@@ -717,6 +717,22 @@ func (t *testEnv) unregisterTask() {
 	}
 }
 
+func (t *testEnv) putTask() {
+	rngs := t.ranges
+	if len(rngs) == 0 {
+		rngs = []kv.KeyRange{{}}
+	}
+	tsk := streamhelper.TaskEvent{
+		Type: streamhelper.EventAdd,
+		Name: "whole",
+		Info: &backup.StreamBackupTaskInfo{
+			Name: "whole",
+		},
+		Ranges: rngs,
+	}
+	t.taskCh <- tsk
+}
+
 func (t *testEnv) ScanLocksInOneRegion(bo *tikv.Backoffer, key []byte, maxVersion uint64, limit uint32) ([]*txnlock.Lock, *tikv.KeyLocation, error) {
 	for _, r := range t.regions {
 		if len(r.locks) != 0 {