*: fix flow control deadlock (release-4.0) (#1779)

cdc/sink/common/flow_control.go

@@ -60,25 +60,28 @@ func (c *TableMemoryQuota) ConsumeWithBlocking(nBytes uint64, blockCallBack func
 		return cerrors.ErrFlowControllerEventLargerThanQuota.GenWithStackByArgs(nBytes, c.Quota)
 	}
 
+	c.mu.Lock()
+	if c.Consumed+nBytes >= c.Quota {
+		c.mu.Unlock()
+		err := blockCallBack()
+		if err != nil {
+			return errors.Trace(err)
+		}
+	} else {
+		c.mu.Unlock()
+	}
+
 	c.mu.Lock()
 	defer c.mu.Unlock()
 
-	calledBack := false
 	for {
 		if atomic.LoadUint32(&c.IsAborted) == 1 {
 			return cerrors.ErrFlowControllerAborted.GenWithStackByArgs()
 		}
+
 		if c.Consumed+nBytes < c.Quota {
 			break
 		}
-
-		if !calledBack {
-			calledBack = true
-			err := blockCallBack()
-			if err != nil {
-				return errors.Trace(err)
-			}
-		}
 		c.cond.Wait()
 	}
 

cdc/sink/common/flow_control_test.go

@@ -417,6 +417,48 @@ func (s *flowControlSuite) TestFlowControlCallBack(c *check.C) {
 	c.Assert(atomic.LoadUint64(&consumedBytes), check.Equals, uint64(0))
 }
 
+func (s *flowControlSuite) TestFlowControlCallBackNotBlockingRelease(c *check.C) {
+	defer testleak.AfterTest(c)()
+
+	var wg sync.WaitGroup
+	controller := NewTableFlowController(512)
+	wg.Add(1)
+
+	ctx, cancel := context.WithCancel(context.TODO())
+	defer cancel()
+
+	go func() {
+		defer wg.Done()
+		err := controller.Consume(1, 511, func() error {
+			c.Fatalf("unreachable")
+			return nil
+		})
+		c.Assert(err, check.IsNil)
+
+		var isBlocked int32
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			<-time.After(time.Second * 1)
+			// makes sure that this test case is valid
+			c.Assert(atomic.LoadInt32(&isBlocked), check.Equals, int32(1))
+			controller.Release(1)
+			cancel()
+		}()
+
+		err = controller.Consume(2, 511, func() error {
+			atomic.StoreInt32(&isBlocked, 1)
+			<-ctx.Done()
+			atomic.StoreInt32(&isBlocked, 0)
+			return ctx.Err()
+		})
+
+		c.Assert(err, check.ErrorMatches, ".*context canceled.*")
+	}()
+
+	wg.Wait()
+}
+
 func (s *flowControlSuite) TestFlowControlCallBackError(c *check.C) {
 	defer testleak.AfterTest(c)()