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x/net/trace: data race using RenderEvents #76402

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x/net/trace: data race using RenderEvents#76402
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BugReportIssues describing a possible bug in the Go implementation.NeedsFixThe path to resolution is known, but the work has not been done.
Milestone
Unreleased
@marefr

Description

@marefr
marefr
opened on Nov 21, 2025

Go version

go version go1.24.1 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/marcus/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/marcus/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/w4/2g0lfwdx05b4n7wcv7wpg9kh0000gn/T/go-build3363630429=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/marcus/go/src/github.com/marefr/enablebankinggo/go.mod'
GOMODCACHE='/Users/marcus/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/marcus/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.24.1/libexec'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/Users/marcus/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.24.1/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

  1. Writing events to event log using golang.org/x/net/trace
  2. Writing a test to verify eventlog was created using trace.RenderEvents(...)
  3. Running tests with race detector enabled

What did you see happen?

WARNING: DATA RACE
Read at 0x00c000095a70 by goroutine 8:
  golang.org/x/net/trace.RenderEvents()
      /home/runner/go/pkg/mod/golang.org/x/[email protected]/trace/events.go:61 +0x171
  github.com/marefr/go-conntrack/providers/trace_test.fetchTraceEvents()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer_test.go:89 +0x284
  github.com/marefr/go-conntrack/providers/trace_test.TestDialerTracingCapturedInPage()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer_test.go:33 +0x29c
  testing.tRunner()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:1934 +0x21c
  testing.(*T).Run.gowrap1()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:1997 +0x44
Details 
==================
WARNING: DATA RACE
Read at 0x00c000095a70 by goroutine 8:
  golang.org/x/net/trace.RenderEvents()
      /home/runner/go/pkg/mod/golang.org/x/[email protected]/trace/events.go:61 +0x171
  github.com/marefr/go-conntrack/providers/trace_test.fetchTraceEvents()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer_test.go:89 +0x284
  github.com/marefr/go-conntrack/providers/trace_test.TestDialerTracingCapturedInPage()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer_test.go:33 +0x29c
  testing.tRunner()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:1934 +0x21c
  testing.(*T).Run.gowrap1()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:1997 +0x44

Previous write at 0x00c000095a70 by goroutine 9:
  runtime.mapassign_faststr()
      /opt/hostedtoolcache/go/1.25.4/x64/src/internal/runtime/maps/runtime_faststr_swiss.go:263 +0x0
  golang.org/x/net/trace.getEventFamily()
      /home/runner/go/pkg/mod/golang.org/x/[email protected]/trace/events.go:162 +0x14f
  golang.org/x/net/trace.NewEventLog()
      /home/runner/go/pkg/mod/golang.org/x/[email protected]/trace/events.go:142 +0x2c5
  github.com/marefr/go-conntrack/providers/trace.trackListenerConnection()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer.go:78 +0x359
  github.com/marefr/go-conntrack/providers/trace.tracer.TrackConnection()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer.go:48 +0xbe
  github.com/marefr/go-conntrack/providers/trace.(*tracer).TrackConnection()
      <autogenerated>:1 +0x64
  github.com/marefr/go-conntrack/v2.(*connTrackListener).Accept()
      /home/runner/work/go-conntrack/go-conntrack/listener_wrapper.go:134 +0xbb1
  net/http.(*onceCloseListener).Accept()
      <autogenerated>:1 +0x43
  net/http.(*Server).Serve()
      /opt/hostedtoolcache/go/1.25.4/x64/src/net/http/server.go:3463 +0x60f
  github.com/marefr/go-conntrack/providers/trace_test.setupServerListener.func2()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer_test.go:77 +0x70

Goroutine 8 (running) created at:
  testing.(*T).Run()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:1997 +0x9d2
  testing.runTests.func1()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:2477 +0x85
  testing.tRunner()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:1934 +0x21c
  testing.runTests()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:2475 +0x96c
  testing.(*M).Run()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:2337 +0xed4
  main.main()
      _testmain.go:49 +0x164

Goroutine 9 (running) created at:
  github.com/marefr/go-conntrack/providers/trace_test.setupServerListener()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer_test.go:76 +0x4a8
  github.com/marefr/go-conntrack/providers/trace_test.TestDialerTracingCapturedInPage()
      /home/runner/work/go-conntrack/go-conntrack/providers/trace/tracer_test.go:26 +0x3e
  testing.tRunner()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:1934 +0x21c
  testing.(*T).Run.gowrap1()
      /opt/hostedtoolcache/go/1.25.4/x64/src/testing/testing.go:1997 +0x44
==================
--- FAIL: TestDialerTracingCapturedInPage (0.02s)
    tracer_test.go:38: stopping http.Server at: 127.0.0.1:43071
    testing.go:1617: race detected during execution of test
FAIL
FAIL	github.com/marefr/go-conntrack/providers/trace	0.037s
FAIL

What did you expect to see?

No data race.

There might be problems with my code, however I did notice what seems like a bug in the following lines as pointed out by data race warning /home/runner/go/pkg/mod/golang.org/x/[email protected]/trace/events.go:61 (code):

data.Families = make([]string, 0, len(families))
famMu.RLock()

I'm pretty sure the read lock should happen before since len(families) is a read, i.e.

famMu.RLock()
data.Families = make([]string, 0, len(families))

My code/test in question here: https://github.com/marefr/go-conntrack/blob/v2-poc/providers/trace/tracer_test.go

Additional information:
I did manually change so that the read lock happens before in events.go and the data race goes away.

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