x/net/http2: data race in TestGoroutineLock

[AlexanderYastrebov]

Go version

go version go1.25.1 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/alexander/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/alexander/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/dd/7b4mqcf91sn1kw0xrq40b13c0000gn/T/go-build3550978080=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/alexander/src/github.com/golang/net/go.mod'
GOMODCACHE='/Users/alexander/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/alexander/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/alexander/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.25.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

git log -1 --oneline
59706cd (HEAD -> master, tag: v0.45.0, origin/master, origin/HEAD) html: impose open element stack size limit

Running

while go test ./http2 -trimpath -race -count=10 ; do echo OK ; done

What did you see happen?

after a while fails with:

==================
WARNING: DATA RACE
Read at 0x000102f0454d by goroutine 68877:
  golang.org/x/net/http2.goroutineLock.checkNotOn()
      golang.org/x/net/http2/gotrack.go:52 +0x2c
  golang.org/x/net/http2.(*serverConn).sendServeMsg()
      golang.org/x/net/http2/server.go:1112 +0x68
  golang.org/x/net/http2.(*serverConn).runHandler.deferwrap1()
      golang.org/x/net/http2/server.go:2400 +0x24
  runtime.deferreturn()
      runtime/panic.go:589 +0x5c
  golang.org/x/net/http2.(*serverConn).scheduleHandler.gowrap1()
      golang.org/x/net/http2/server.go:2359 +0x50

Previous write at 0x000102f0454d by goroutine 72175:
  golang.org/x/net/http2.TestGoroutineLock.func1()
      golang.org/x/net/http2/gotrack_test.go:16 +0x30
  runtime.deferreturn()
      runtime/panic.go:589 +0x5c
  testing.tRunner()
      testing/testing.go:1934 +0x164
  testing.(*T).Run.gowrap1()
      testing/testing.go:1997 +0x3c

Goroutine 68877 (running) created at:
  golang.org/x/net/http2.(*serverConn).scheduleHandler()
      golang.org/x/net/http2/server.go:2359 +0x1c0
  golang.org/x/net/http2.(*serverConn).processHeaders()
      golang.org/x/net/http2/server.go:2116 +0x90c
  golang.org/x/net/http2.(*serverConn).processFrame()
      golang.org/x/net/http2/server.go:1609 +0x2c8
  golang.org/x/net/http2.(*serverConn).processFrameFromReader()
      golang.org/x/net/http2/server.go:1547 +0x260
  golang.org/x/net/http2.(*serverConn).serve()
      golang.org/x/net/http2/server.go:1003 +0x1100
  golang.org/x/net/http2.(*Server).serveConn()
      golang.org/x/net/http2/server.go:565 +0x133c
  golang.org/x/net/http2.(*Server).ServeConn()
      golang.org/x/net/http2/server.go:424 +0x160
  golang.org/x/net/http2.ConfigureServer.func2()
      golang.org/x/net/http2/server.go:321 +0xc8
  golang.org/x/net/http2.ConfigureServer.func3()
      golang.org/x/net/http2/server.go:329 +0x60
  net/http.(*conn).serve()
      net/http/server.go:1996 +0x1834
  net/http.(*Server).Serve.gowrap3()
      net/http/server.go:3493 +0x48

Goroutine 72175 (finished) created at:
  testing.(*T).Run()
      testing/testing.go:1997 +0x6e0
  testing.runTests.func1()
      testing/testing.go:2477 +0x74
  testing.tRunner()
      testing/testing.go:1934 +0x164
  testing.runTests()
      testing/testing.go:2475 +0x734
  testing.(*M).Run()
      testing/testing.go:2337 +0xaf4
  main.main()
      _testmain.go:875 +0x100
==================
--- FAIL: TestNoUnicodeStrings (0.21s)
    testing.go:1617: race detected during execution of test
FAIL
FAIL    golang.org/x/net/http2  35.427s

Note that it points to TestNoUnicodeStrings while race is in the TestGoroutineLock.

What did you expect to see?

No test failure.

This is potentially related to #66519 and https://go-review.googlesource.com/c/net/+/701836

[dmitshur]

Thanks for the report. How quickly does it typically reproduce for you? Also, to confirm, does git status print that there are no local code changes for you? In my case, 10 minutes of running didn't trigger the issue. (Though there were some other occasional flakes that I skipped over to try to repro this.)

From looking briefly, I'm not sure how this can happen given I'm not seeing parallel test execution in the x/net/http2 package, so I wonder what caused the http.Server.Serve goroutine to be running at the same time as TestGoroutineLock. Could it be that some other test isn't cleaning up after itself?

CC @neild, @tombergan.

[dmitshur]

Oh, trying the same repro on a different darwin/arm64 machine, this reproduced within a minute 3 out of 3 times. Unless it's a coincidence, the only difference is that the no-repro machine has M1 Pro and macOS 15.7.1, the yes-repro machine has M4 Pro and macOS 26.0.1 and close to out of the box software.

[neild]

Thanks. https://go.dev/cl/710675 should fix this.

[gopherbot]

Change https://go.dev/cl/710675 mentions this issue: http2: avoid data race on DebugGoroutines in TestGoroutineLock