data race in buildSamplingStats

[zhouqiang-cl]

Bug Report

[2021-06-08T13:05:46.842Z] WARNING: DATA RACE
[2021-06-08T13:05:46.842Z] Read at 0x00c07d8b16d8 by goroutine 527:
[2021-06-08T13:05:46.842Z]   github.com/pingcap/tidb/executor.(*AnalyzeColumnsExec).buildSamplingStats()
[2021-06-08T13:05:46.842Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/analyze.go:891 +0x1164
[2021-06-08T13:05:46.842Z]   github.com/pingcap/tidb/executor.analyzeColumnsPushdown()
[2021-06-08T13:05:46.842Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/analyze.go:607 +0x853
[2021-06-08T13:05:46.842Z]   github.com/pingcap/tidb/executor.(*AnalyzeExec).analyzeWorker()
[2021-06-08T13:05:46.842Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/analyze.go:279 +0x3e4
[2021-06-08T13:05:46.842Z] 
[2021-06-08T13:05:46.842Z] Previous write at 0x00c07d8b16d8 by goroutine 795:
[2021-06-08T13:05:46.842Z]   github.com/pingcap/tidb/executor.(*AnalyzeColumnsExec).handleNDVForSpecialIndexes()
[2021-06-08T13:05:46.842Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/analyze.go:1028 +0x251
[2021-06-08T13:05:46.842Z] 
[2021-06-08T13:05:46.842Z] Goroutine 527 (running) created at:
[2021-06-08T13:05:46.842Z]   github.com/pingcap/tidb/executor.(*AnalyzeExec).Next()
[2021-06-08T13:05:46.842Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/analyze.go:93 +0x1c4
[2021-06-08T13:05:46.842Z]   github.com/pingcap/tidb/executor.Next()
[2021-06-08T13:05:46.842Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/executor.go:286 +0x2a8
[2021-06-08T13:05:46.842Z]   github.com/pingcap/tidb/executor.(*ExecStmt).handleNoDelayExecutor()
[2021-06-08T13:05:46.842Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/adapter.go:586 +0x3bc
[2021-06-08T13:05:46.842Z]   github.com/pingcap/tidb/executor.(*ExecStmt).handleNoDelay()
[2021-06-08T13:05:46.842Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/adapter.go:467 +0x276
[2021-06-08T13:05:46.843Z]   github.com/pingcap/tidb/executor.(*ExecStmt).Exec()
[2021-06-08T13:05:46.843Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/adapter.go:416 +0x63a
[2021-06-08T13:05:46.843Z]   github.com/pingcap/tidb/session.runStmt()
[2021-06-08T13:05:46.843Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/session/session.go:1653 +0x323
[2021-06-08T13:05:46.843Z]   github.com/pingcap/tidb/session.(*session).ExecuteStmt()
[2021-06-08T13:05:46.843Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/session/session.go:1548 +0xc37
[2021-06-08T13:05:46.843Z]   github.com/pingcap/tidb/util/testkit.(*TestKit).Exec()
[2021-06-08T13:05:46.843Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/util/testkit/testkit.go:170 +0x2fc
[2021-06-08T13:05:46.843Z]   github.com/pingcap/tidb/util/testkit.(*TestKit).MustExec()
[2021-06-08T13:05:46.843Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/util/testkit/testkit.go:216 +0x96
[2021-06-08T13:05:46.843Z]   github.com/pingcap/tidb/executor_test.(*testSuite1).TestAnalyzeFullSamplingOnIndexWithVirtualColumnOrPrefixColumn()
[2021-06-08T13:05:46.843Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/analyze_test.go:992 +0x1ec
[2021-06-08T13:05:46.843Z]   runtime.call16()
[2021-06-08T13:05:46.843Z]       /usr/local/go/src/runtime/asm_amd64.s:550 +0x3d
[2021-06-08T13:05:46.843Z]   reflect.Value.Call()
[2021-06-08T13:05:46.843Z]       /usr/local/go/src/reflect/value.go:337 +0xd8
[2021-06-08T13:05:46.843Z]   github.com/pingcap/check.(*suiteRunner).forkTest.func1()
[2021-06-08T13:05:46.843Z]       /nfs/cache/mod/github.com/pingcap/check@v0.0.0-20200212061837-5e12011dc712/check.go:850 +0xb3b
[2021-06-08T13:05:46.843Z]   github.com/pingcap/check.(*suiteRunner).forkCall.func1()
[2021-06-08T13:05:46.843Z]       /nfs/cache/mod/github.com/pingcap/check@v0.0.0-20200212061837-5e12011dc712/check.go:739 +0x11d
[2021-06-08T13:05:46.843Z] 
[2021-06-08T13:05:46.843Z] Goroutine 795 (running) created at:
[2021-06-08T13:05:46.843Z]   github.com/pingcap/tidb/executor.analyzeColumnsPushdown()
[2021-06-08T13:05:46.843Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/analyze.go:606 +0x7db
[2021-06-08T13:05:46.843Z]   github.com/pingcap/tidb/executor.(*AnalyzeExec).analyzeWorker()
[2021-06-08T13:05:46.843Z]       /home/jenkins/agent/workspace/tidb-unit-test-nightly/go/src/github.com/pingcap/tidb/executor/analyze.go:279 +0x3e4

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

in ci https://ci.pingcap.net/blue/rest/organizations/jenkins/pipelines/tidb-unit-test-nightly/runs/276/nodes/104/steps/408/log/?start=0

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

master f81ef55

[winoros]

This log is rather strange.
Line 891 is

err = e.decodeSampleDataWithVirtualColumn(rootRowCollector, fieldTps, virtualColIdx, e.schemaForVirtualColEval)

Line 1028 is

e.subIndexWorkerWg = &sync.WaitGroup{}

We found not see any chance that they might cause data race.

[winoros]

The lines' content would not change if we make failpoint-enable so we're curious how the data race happens.

[bb7133]

I think we can check if it is reproduced again.

[winoros]

This it's bug caused by golang, changed in https://github.com/pingcap/tidb/pull/25789/files#diff-242b6560708c7b355e87f16df635a3b0d235ff9f12fe72456738db8df30d8ee0R599
It really strange.

[ti-srebot]

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