send on closed channel in the TestGetDefaultValueOfColumn

[hawkingrei]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

2. What did you expect to see? (Required)

3. What did you see instead (Required)

==================
WARNING: DATA RACE
Read at 0x00c04b5a57b0 by goroutine 423780:
  runtime.chansend()
      GOROOT/src/runtime/chan.go:160 +0x0
  github.com/pingcap/tidb/ddl.(*backfillWorker).run.func1()
      ddl/backfilling.go:450 +0x14a
  github.com/pingcap/tidb/util.Recover()
      util/misc.go:114 +0xa9
  github.com/pingcap/tidb/ddl.(*backfillWorker).run.func2()
      ddl/backfilling.go:449 +0x54
  runtime.gopanic()
      GOROOT/src/runtime/panic.go:890 +0x262
  github.com/pingcap/tidb/ddl.(*backfillWorker).handleBackfillTask()
      ddl/backfilling.go:327 +0x49c
  github.com/pingcap/tidb/ddl.(*backfillWorker).run()
      ddl/backfilling.go:486 +0xa54
  github.com/pingcap/tidb/ddl.(*backfillScheduler).adjustWorkerSize.func1()
      ddl/backfilling_scheduler.go:202 +0x71
Previous write at 0x00c04b5a57b0 by goroutine 423772:
  runtime.closechan()
      GOROOT/src/runtime/chan.go:357 +0x0
  github.com/pingcap/tidb/ddl.(*backfillScheduler).close()
      ddl/backfilling_scheduler.go:263 +0x137
  github.com/pingcap/tidb/ddl.(*ddlCtx).writePhysicalTableRecord()
      ddl/backfilling.go:870 +0x14b3
  github.com/pingcap/tidb/ddl.(*worker).addPhysicalTableIndex()
      ddl/index.go:1928 +0x574
  github.com/pingcap/tidb/ddl.(*worker).addTableIndex()
      ddl/index.go:1958 +0x147
  github.com/pingcap/tidb/ddl.runReorgJobAndHandleErr.func1()
      ddl/index.go:993 +0x131
  github.com/pingcap/tidb/ddl.(*worker).runReorgJob.func1()
      ddl/reorg.go:210 +0x92
Goroutine 423780 (running) created at:
  github.com/pingcap/tidb/ddl.(*backfillScheduler).adjustWorkerSize()
      ddl/backfilling_scheduler.go:202 +0x124a
  github.com/pingcap/tidb/ddl.(*ddlCtx).writePhysicalTableRecord()
      ddl/backfilling.go:835 +0xc9e
  github.com/pingcap/tidb/ddl.(*worker).addPhysicalTableIndex()
      ddl/index.go:1928 +0x574
  github.com/pingcap/tidb/ddl.(*worker).addTableIndex()
      ddl/index.go:1958 +0x147
  github.com/pingcap/tidb/ddl.runReorgJobAndHandleErr.func1()
      ddl/index.go:993 +0x131
  github.com/pingcap/tidb/ddl.(*worker).runReorgJob.func1()
      ddl/reorg.go:210 +0x92
Goroutine 423772 (finished) created at:
  github.com/pingcap/tidb/ddl.(*worker).runReorgJob()
      ddl/reorg.go:208 +0x645
  github.com/pingcap/tidb/ddl.runReorgJobAndHandleErr()
      ddl/index.go:988 +0x79d
  github.com/pingcap/tidb/ddl.doReorgWorkForCreateIndex()
      ddl/index.go:818 +0xbc7
  github.com/pingcap/tidb/ddl.(*worker).onCreateIndex()
      ddl/index.go:676 +0x11ee
  github.com/pingcap/tidb/ddl.(*worker).runDDLJob()
      ddl/ddl_worker.go:1024 +0x7f5
  github.com/pingcap/tidb/ddl.(*worker).HandleDDLJobTable()
      ddl/ddl_worker.go:768 +0x691
  github.com/pingcap/tidb/ddl.(*ddl).delivery2worker.func1()
      ddl/job_table.go:285 +0xb65
  github.com/pingcap/tidb/util.(*WaitGroupWrapper).Run.func1()
      util/wait_group_wrapper.go:154 +0x73
==================
panic: panic test [recovered]
	panic: send on closed channel
goroutine 423783 [running]:
github.com/pingcap/tidb/ddl.(*backfillWorker).run.func1()
	ddl/backfilling.go:450 +0x14b
github.com/pingcap/tidb/util.Recover({0x6f54012, 0x3}, {0x6f84eae, 0x12}, 0xc0292b3d58, 0x0)
	util/misc.go:114 +0xaa
panic({0x68637c0, 0x87aac00})
	GOROOT/src/runtime/panic.go:890 +0x263
github.com/pingcap/tidb/ddl.(*addIndexTxnWorker).BackfillData(0xc04b1b9c20, {0x0, {0x7f71c130eda8, 0xc04b3bd440}, 0x0, {0xc04b5ba200, 0x13, 0x100}, {0xc04b5f6210, 0x13, ...}, ...})
	ddl/index.go:1847 +0x4a6
github.com/pingcap/tidb/ddl.(*backfillWorker).handleBackfillTask(0xc04b5a7640, 0x2c?, 0xc04b5d2880, {0x87f1b20, 0xc04b1b9c20})
	ddl/backfilling.go:327 +0x49d
github.com/pingcap/tidb/ddl.(*backfillWorker).run(0xc04b5a7640, 0xc04b5b0f58?, {0x87f1b20, 0xc04b1b9c20}, 0xc04b17ea20)
	ddl/backfilling.go:486 +0xa55
created by github.com/pingcap/tidb/ddl.(*backfillScheduler).adjustWorkerSize
	ddl/backfilling_scheduler.go:202 +0x124b 

4. What is your TiDB version? (Required)

[hawkingrei]

https://prow.hawkingrei.com/view/gs/prowpingcap/logs/tidb_race/1640670207598923776