cmd/go: data race when running test with coverprofile #56006
Description
What version of Go are you using (go version)?
$ go version go version devel go1.20-1888875182 Sun Oct 2 15:42:47 2022 +0700 linux/amd64
Does this issue reproduce with the latest release?
No.
What operating system and processor architecture are you using (go env)?
go env Output
$ go env GO111MODULE="on" GOARCH="amd64" GOBIN="/home/ms/go/bin" GOCACHE="/home/ms/.cache/go-build" GOENV="/home/ms/.config/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="linux" GOINSECURE="" GOMODCACHE="/home/ms/go/pkg/mod" GONOPROXY="github.com/tokenomy" GONOSUMDB="github.com/tokenomy" GOOS="linux" GOPATH="/home/ms/go" GOPRIVATE="github.com/tokenomy" GOPROXY="https://proxy.golang.org,direct" GOROOT="/home/ms/opt/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/home/ms/opt/go/pkg/tool/linux_amd64" GOVCS="" GOVERSION="devel go1.20-2807afbac6 Sun Oct 2 15:42:47 2022 +0700" GCCGO="gccgo" GOAMD64="v1" AR="ar" CC="gcc" CXX="g++" CGO_ENABLED="0" GOMOD="/dev/null" GOWORK="" CGO_CFLAGS="-g -O2" CGO_CPPFLAGS="" CGO_CXXFLAGS="-g -O2" CGO_FFLAGS="-g -O2" CGO_LDFLAGS="-g -O2" PKG_CONFIG="pkg-config" GOGCCFLAGS="-fPIC -m64 -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3580077936=/tmp/go-build -gno-record-gcc-switches"
What did you do?
I run go test with -race and -coverprofile at the same time on github.com/shuLhan/share and the test are FAIL with data race.
$ CGO_ENABLED=1 go test -failfast -race -count=1 -coverprofile=cover.out ./...
...
==================
WARNING: DATA RACE
Read at 0x000001e5f04c by main goroutine:
internal/coverage/encodecounter.(*CoverageDataWriter).writeCounters.func2()
/home/ms/opt/go/src/internal/coverage/encodecounter/encode.go:261 +0x11c
runtime/coverage.(*emitState).VisitFuncs()
/home/ms/opt/go/src/runtime/coverage/emit.go:539 +0x6bc
internal/coverage/encodecounter.(*CoverageDataWriter).writeCounters()
/home/ms/opt/go/src/internal/coverage/encodecounter/encode.go:268 +0x16f
internal/coverage/encodecounter.(*CoverageDataWriter).AppendSegment()
/home/ms/opt/go/src/internal/coverage/encodecounter/encode.go:175 +0x8ea
internal/coverage/encodecounter.(*CoverageDataWriter).Write()
/home/ms/opt/go/src/internal/coverage/encodecounter/encode.go:71 +0x97
runtime/coverage.(*emitState).emitCounterDataFile()
/home/ms/opt/go/src/runtime/coverage/emit.go:573 +0x91
runtime/coverage.emitCounterDataToDirectory()
/home/ms/opt/go/src/runtime/coverage/emit.go:322 +0x310
runtime/coverage.processCoverTestDir()
/home/ms/opt/go/src/runtime/coverage/testsupport.go:39 +0x1c4
main.coverTearDown()
_testmain.go:179 +0x159
testing.coverReport2()
/home/ms/opt/go/src/testing/newcover.go:37 +0xcb
testing.coverReport()
/home/ms/opt/go/src/testing/cover.go:83 +0xc74
testing.(*M).writeProfiles()
/home/ms/opt/go/src/testing/testing.go:2053 +0xc6f
testing.(*M).after.func1()
/home/ms/opt/go/src/testing/testing.go:1987 +0x30
sync.(*Once).doSlow()
/home/ms/opt/go/src/sync/once.go:74 +0x101
sync.(*Once).Do()
/home/ms/opt/go/src/sync/once.go:65 +0x46
testing.(*M).after()
/home/ms/opt/go/src/testing/testing.go:1986 +0x55
testing.(*M).Run.func4()
/home/ms/opt/go/src/testing/testing.go:1761 +0x39
runtime.deferreturn()
/home/ms/opt/go/src/runtime/panic.go:476 +0x32
testing.(*M).Run()
/home/ms/opt/go/src/testing/testing.go:1771 +0xbb3
github.com/shuLhan/share/lib/dns.TestMain()
/home/ms/go/src/github.com/shuLhan/share/lib/dns/dns_test.go:63 +0x5db
main.main()
_testmain.go:192 +0x33d
Previous write at 0x000001e5f04c by goroutine 9:
sync/atomic.AddInt32()
/home/ms/opt/go/src/runtime/race_amd64.s:281 +0xb
sync/atomic.AddUint32()
<autogenerated>:1 +0x1a
github.com/shuLhan/share/lib/dns.(*Server).processRequest()
/home/ms/go/src/github.com/shuLhan/share/lib/dns/server.go:593 +0xc67
github.com/shuLhan/share/lib/dns.(*Server).ListenAndServe.func1()
/home/ms/go/src/github.com/shuLhan/share/lib/dns/server.go:187 +0x39
Goroutine 9 (running) created at:
github.com/shuLhan/share/lib/dns.(*Server).ListenAndServe()
/home/ms/go/src/github.com/shuLhan/share/lib/dns/server.go:187 +0xe6
github.com/shuLhan/share/lib/dns.TestMain.func1()
/home/ms/go/src/github.com/shuLhan/share/lib/dns/dns_test.go:54 +0x44
==================
...
There are many lines like that with the same pattern.
In the above snippet, the lib/dns/dns_test.go:63 point this code [1],
os.Exit(m.Run())
inside the TestMain. So it does not make sense if the data race is in my code.
A quick bisect point to this commit [2].
I run the test using GOEXPERIMENT=coverageredesign flag using Go tip commit 53773a5
$ go version
go version devel go1.20-53773a5d08 Wed Sep 28 11:50:58 2022 +0000 linux/amd64
Without GOEXPERIMENT flag,
$ CGO_ENABLED=1 go test -race -coverprofile=cover.out ./lib/dns
ok github.com/shuLhan/share/lib/dns 0.707s coverage: 56.8% of statements
With GOEXPERIMENT=coverageredesign flag,
$ GOEXPERIMENT=coverageredesign CGO_ENABLED=1 go test -race ./lib/dns
ok github.com/shuLhan/share/lib/dns 0.683s
$ GOEXPERIMENT=coverageredesign CGO_ENABLED=1 go test -race -coverprofile=cover.out ./lib/dns
dns.Server: listening for DNS over TLS at 127.0.0.1:18053
dns.Server: listening for DNS over TCP at 127.0.0.1:5300
dns.Server: listening for DNS over UDP at 127.0.0.1:5300
dns.Server: listening for DNS over HTTPS at 127.0.0.1:8443
dns: invalid IP address "localhost"
dns: invalid name server URI "://127.0.0.1"
dns: invalid IP address "localhost:53"
dns: invalid IP address "localhost:53"
PASS
==================
WARNING: DATA RACE
Read at 0x000001e5f04c by main goroutine:
internal/coverage/encodecounter.(*CoverageDataWriter).writeCounters.func2()
/home/ms/opt/go/src/internal/coverage/encodecounter/encode.go:261 +0x11c
runtime/coverage.(*emitState).VisitFuncs()
/home/ms/opt/go/src/runtime/coverage/emit.go:539 +0x6bc
internal/coverage/encodecounter.(*CoverageDataWriter).writeCounters()
/home/ms/opt/go/src/internal/coverage/encodecounter/encode.go:268 +0x16f
...
[1] https://github.com/shuLhan/share/blob/61720a183756bdf5a8af45e7d75116ce7ef188e0/lib/dns/dns_test.go#L63
[2] https://go.googlesource.com/go/+/53773a5d0892be4489b4d5e91bbc8ae61000ada7%5E%21/
What did you expect to see?
All test running succesfully.
What did you see instead?
Some test are FAIL-ed due to data race but point to code that are not relevant (in this case the race is inside TestMain function).