DATA RACE in the TestDDLCallback

[hawkingrei]

Bug Report

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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 0x00c00bd3c768 by goroutine 27534:
  github.com/pingcap/tidb/ddl/util/callback.(*TestDDLCallback).OnGetJobBefore()
      ddl/util/callback/callback.go:145 +0x48
  github.com/pingcap/tidb/ddl.(*ddl).loadDDLJobAndRun()
      ddl/job_table.go:357 +0x3e2
  github.com/pingcap/tidb/ddl.(*ddl).startDispatchLoop()
      ddl/job_table.go:301 +0xc70
  github.com/pingcap/tidb/ddl.(*ddl).startDispatchLoop-fm()
      <autogenerated>:1 +0x39
  github.com/pingcap/tidb/util.(*WaitGroupWrapper).Run.func1()
      util/wait_group_wrapper.go:154 +0x73
Previous write at 0x00c00bd3c768 by goroutine 48:
  ddl/pausetest/pausetest_test.TestResumeJobPositive()
      ddl/pausetest/pause_test.go:466 +0xaa8
  github.com/pingcap/tidb/session.runStmt()
      session/session.go:2400 +0x62f
  github.com/pingcap/tidb/session.(*session).ExecuteStmt()
      session/session.go:2250 +0x1405
  github.com/pingcap/tidb/testkit.(*TestKit).ExecWithContext()
      testkit/testkit.go:324 +0x8ae
  github.com/pingcap/tidb/testkit.(*TestKit).MustExecWithContext()
      testkit/testkit.go:132 +0xb7
  github.com/pingcap/tidb/testkit.(*TestKit).MustExec()
      testkit/testkit.go:127 +0x138
  ddl/pausetest/pausetest_test.TestResumeJobPositive()
      ddl/pausetest/pause_test.go:431 +0x207
  github.com/pingcap/tidb/session.runStmt()
      session/session.go:2400 +0x62f
  github.com/pingcap/tidb/session.(*session).ExecuteStmt()
      session/session.go:2250 +0x1405
  github.com/pingcap/tidb/testkit.(*TestKit).ExecWithContext()
      testkit/testkit.go:324 +0x8ae
  github.com/pingcap/tidb/testkit.(*TestKit).MustExecWithContext()
      testkit/testkit.go:132 +0xb7
  github.com/pingcap/tidb/testkit.(*TestKit).MustExec()
      testkit/testkit.go:127 +0x138
  ddl/pausetest/pausetest_test.TestResumeJobPositive()
      ddl/pausetest/pause_test.go:430 +0x1e7
  github.com/pingcap/tidb/domain.(*Domain).rebuildSysVarCache()
      domain/sysvar_cache.go:146 +0x8c4
  github.com/pingcap/tidb/domain.(*Domain).LoadSysVarCacheLoop()
      domain/domain.go:1774 +0xa8
  github.com/pingcap/tidb/session.bootstrapSessionImpl()
      session/session.go:3357 +0x6e4
  github.com/pingcap/tidb/domain.(*Domain).GetSessionCache()
      domain/sysvar_cache.go:62 +0x5c
  github.com/pingcap/tidb/session.(*session).loadCommonGlobalVariablesIfNeeded()
      session/session.go:3721 +0x104
  github.com/pingcap/tidb/session.(*session).ExecuteStmt()
      session/session.go:2130 +0x145
  github.com/pingcap/tidb/session.(*session).ExecuteInternal()
      session/session.go:1666 +0x31b
  github.com/pingcap/tidb/domain.(*Domain).LoadPrivilegeLoop()
      domain/domain.go:1717 +0x130
  github.com/pingcap/tidb/session.bootstrapSessionImpl()
      session/session.go:3350 +0x687
  github.com/pingcap/tidb/session.BootstrapSession()
      session/session.go:3271 +0xb4
  github.com/pingcap/tidb/testkit.bootstrap()
      testkit/mockstore.go:218 +0x9b
  github.com/pingcap/tidb/testkit.CreateMockStoreAndDomainWithSchemaLease()
      testkit/mockstore.go:243 +0xe9
  ddl/pausetest/pausetest_test.TestResumeJobPositive()
      ddl/pausetest/pause_test.go:400 +0x5d
  testing.tRunner()
      GOROOT/src/testing/testing.go:1576 +0x216
  testing.(*T).Run.func1()
      GOROOT/src/testing/testing.go:1629 +0x47
Goroutine 27534 (running) created at:
  github.com/pingcap/tidb/util.(*WaitGroupWrapper).Run()
      util/wait_group_wrapper.go:152 +0xe4
  github.com/pingcap/tidb/ddl.(*ddl).prepareWorkers4ConcurrencyDDL()
      ddl/ddl.go:756 +0x4a9
  github.com/pingcap/tidb/ddl.(*ddl).Start()
      ddl/ddl.go:782 +0x8be
  github.com/pingcap/tidb/domain.(*Domain).Init()
      domain/domain.go:1206 +0x16cc
  github.com/pingcap/tidb/session.(*domainMap).Get.func1()
      session/tidb.go:93 +0x676
  github.com/pingcap/tidb/util.RunWithRetry()
      util/misc.go:69 +0x93
  github.com/pingcap/tidb/session.(*domainMap).Get()
      session/tidb.go:79 +0x2d2
  github.com/pingcap/tidb/session.createSessionWithOpt()
      session/session.go:3578 +0x75
  github.com/pingcap/tidb/session.createSession()
      session/session.go:3570 +0x38
  github.com/pingcap/tidb/session.createSessionsImpl()
      session/session.go:3555 +0x81
  github.com/pingcap/tidb/session.createSessions()
      session/session.go:3542 +0x4b
  github.com/pingcap/tidb/session.bootstrapSessionImpl()
      session/session.go:3317 +0x3e6
  github.com/pingcap/tidb/session.BootstrapSession()
      session/session.go:3271 +0xb4
  github.com/pingcap/tidb/testkit.bootstrap()
      testkit/mockstore.go:218 +0x9b
  github.com/pingcap/tidb/testkit.CreateMockStoreAndDomainWithSchemaLease()
      testkit/mockstore.go:243 +0xe9
  ddl/pausetest/pausetest_test.TestResumeJobPositive()
      ddl/pausetest/pause_test.go:400 +0x5d
  testing.tRunner()
      GOROOT/src/testing/testing.go:1576 +0x216
  testing.(*T).Run.func1()
      GOROOT/src/testing/testing.go:1629 +0x47
Goroutine 48 (running) created at:
  testing.(*T).Run()
      GOROOT/src/testing/testing.go:1629 +0x805
  testing.runTests.func1()
      GOROOT/src/testing/testing.go:2036 +0x8d
  testing.tRunner()
      GOROOT/src/testing/testing.go:1576 +0x216
  testing.runTests()
      GOROOT/src/testing/testing.go:2034 +0x87c
  testing.(*M).Run()
      GOROOT/src/testing/testing.go:1906 +0xb44
  go.uber.org/goleak.VerifyTestMain()
      external/org_uber_go_goleak/testmain.go:53 +0x70
  ddl/pausetest/pausetest_test.TestMain()
      ddl/pausetest/main_test.go:44 +0x45c
  main.main()
      bazel-out/k8-fastbuild/bin/ddl/pausetest/pausetest_test_/testmain.go:108 +0x5e8
================== 

4. What is your TiDB version? (Required)