DATA RACE in ttlworker.(*taskManager).resizeDelWorkers

[hawkingrei]

Bug Report

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1. Minimal reproduce step (Required)

==================
WARNING: DATA RACE
Read at 0x00c013c04558 by goroutine 111298:
  github.com/pingcap/tidb/ttl/ttlworker.(*taskManager).resizeDelWorkers()
      ttl/ttlworker/task_manager.go:169 +0x64
  github.com/pingcap/tidb/ttl/ttlworker.(*taskManager).resizeWorkersWithSysVar()
      ttl/ttlworker/task_manager.go:109 +0x224
  github.com/pingcap/tidb/ttl/ttlworker.(*taskManager).ResizeWorkersWithSysVar()
      ttl/ttlworker/task_manager_test.go:44 +0x151
  github.com/pingcap/tidb/ttl/ttlworker_test.TestTriggerScanTask()
      ttl/ttlworker/job_manager_integration_test.go:442 +0x13d
  github.com/pingcap/tidb/domain.(*Domain).rebuildSysVarCache()
      domain/sysvar_cache.go:146 +0x844
  github.com/pingcap/tidb/domain.(*Domain).LoadSysVarCacheLoop()
      domain/domain.go:1384 +0xa8
  github.com/pingcap/tidb/session.BootstrapSession()
      session/session.go:3337 +0x693
  github.com/pingcap/tidb/domain.(*Domain).GetSessionCache()
      domain/sysvar_cache.go:62 +0x59
  github.com/pingcap/tidb/session.(*session).loadCommonGlobalVariablesIfNeeded()
      session/session.go:3656 +0x104
  github.com/pingcap/tidb/session.(*session).ExecuteStmt()
      session/session.go:2134 +0x2a5
  github.com/pingcap/tidb/session.(*session).ExecuteInternal()
      session/session.go:1668 +0x471
  github.com/pingcap/tidb/domain.(*Domain).LoadPrivilegeLoop()
      domain/domain.go:1328 +0x130
  github.com/pingcap/tidb/session.BootstrapSession()
      session/session.go:3330 +0x644
  github.com/pingcap/tidb/testkit.bootstrap()
      testkit/mockstore.go:85 +0xac
  github.com/pingcap/tidb/testkit.CreateMockStoreAndDomain()
      testkit/mockstore.go:70 +0xe9
  github.com/pingcap/tidb/ttl/ttlworker_test.TestTriggerScanTask()
      ttl/ttlworker/job_manager_integration_test.go:434 +0x58
  testing.tRunner()
      GOROOT/src/testing/testing.go:1446 +0x216
  testing.(*T).Run.func1()
      GOROOT/src/testing/testing.go:1493 +0x47
Previous write at 0x00c013c04558 by goroutine 124348:
  github.com/pingcap/tidb/ttl/ttlworker.(*taskManager).resizeDelWorkers()
      ttl/ttlworker/task_manager.go:169 +0xaa
  github.com/pingcap/tidb/ttl/ttlworker.(*taskManager).resizeWorkersWithSysVar()
      ttl/ttlworker/task_manager.go:109 +0x224
  github.com/pingcap/tidb/ttl/ttlworker.(*JobManager).jobLoop()
      ttl/ttlworker/job_manager.go:159 +0x50d
  github.com/pingcap/tidb/ttl/ttlworker.(*JobManager).jobLoop-fm()
      <autogenerated>:1 +0x39
  github.com/pingcap/tidb/ttl/ttlworker.(*baseWorker).loop()
      ttl/ttlworker/worker.go:134 +0xa3
  github.com/pingcap/tidb/ttl/ttlworker.(*baseWorker).loop-fm()
      <autogenerated>:1 +0x39
  github.com/pingcap/tidb/util.(*WaitGroupWrapper).Run.func1()
      util/wait_group_wrapper.go:154 +0x73
Goroutine 111298 (running) created at:
  testing.(*T).Run()
      GOROOT/src/testing/testing.go:1493 +0x75d
  testing.runTests.func1()
      GOROOT/src/testing/testing.go:1846 +0x99
  testing.tRunner()
      GOROOT/src/testing/testing.go:1446 +0x216
  testing.runTests()
      GOROOT/src/testing/testing.go:1844 +0x7ec
  testing.(*M).Run()
      GOROOT/src/testing/testing.go:1726 +0xa84
  main.main()
      bazel-out/k8-fastbuild/bin/ttl/ttlworker/ttlworker_test_/testmain.go:148 +0x5d0
Goroutine 124348 (running) created at:
  github.com/pingcap/tidb/util.(*WaitGroupWrapper).Run()
      util/wait_group_wrapper.go:152 +0xe4
  github.com/pingcap/tidb/ttl/ttlworker.(*baseWorker).Start()
      ttl/ttlworker/worker.go:71 +0x12d
  github.com/pingcap/tidb/domain.(*Domain).StartTTLJobManager.func1()
      domain/domain.go:2498 +0x1a4
  github.com/pingcap/tidb/util.(*WaitGroupEnhancedWrapper).Run.func1()
      util/wait_group_wrapper.go:96 +0xb7 

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)