[BUG]: Data race issue with span

[jachym-tousek-keboola]

Tracer Version(s)

1.72.1

Go Version(s)

1.24.0

Bug Report

Lately we're seeing data race errors in our logs.

Read:

dd-trace-go/ddtrace/tracer/tracer.go

Line 687 in 94c7f0e

labels = append(labels, traceprof.TraceEndpoint, localRootSpan.Resource)

Write:

dd-trace-go/ddtrace/tracer/span.go

Line 405 in 94c7f0e

s.Resource = v

The write side seems to have a lock from here:

dd-trace-go/ddtrace/tracer/span.go

Lines 117 to 118 in 94c7f0e

	s.Lock()
	defer s.Unlock()

My guess is that applyPPROFLabels is missing localRootSpan.RLock()? Should I send a pull request that would add it?

Reproduction Code

No response

Error Logs

No response

Go Env Output

No response

[nsrip-dd]

Thanks for reporting this issue! I can reproduce this with this test:

func TestPPROFLabelRootSpanRace(t *testing.T) {
	tracer, _, _, stop := startTestTracer(t)
	defer stop()
	parent := tracer.StartSpan("parent")
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		for i := 0; i < 1000; i++ {
			tracer.StartSpan("child", ChildOf(parent.Context()))
		}
	}()
	wg.Add(1)
	go func() {
		defer wg.Done()
		for i := 0; i < 1000; i++ {
			parent.SetTag(ext.ResourceName, "x")
		}
	}()
	wg.Wait()
}

Taking a read lock on the parent span makes sense to me as a fix. Please feel free to send a PR :)