From 3b23d576ea72235a3fef8f157eb5ab76e65854a8 Mon Sep 17 00:00:00 2001
From: Damien Neil <dneil@google.com>
Date: Mon, 8 Sep 2025 15:59:32 -0700
Subject: [PATCH] http2: fix race condition when disabling goroutine debugging
 for one test

Fixes golang/go#66519

Change-Id: I7aecf20db44caaaf49754d62db193b8c42f3c63a
Reviewed-on: https://go-review.googlesource.com/c/net/+/701836
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
---
 http2/gotrack.go     | 17 ++++++++++++++---
 http2/server_test.go |  7 ++++---
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/http2/gotrack.go b/http2/gotrack.go
index 9933c9f8..9921ca09 100644
--- a/http2/gotrack.go
+++ b/http2/gotrack.go
@@ -15,21 +15,32 @@ import (
 	"runtime"
 	"strconv"
 	"sync"
+	"sync/atomic"
 )
 
 var DebugGoroutines = os.Getenv("DEBUG_HTTP2_GOROUTINES") == "1"
 
+// Setting DebugGoroutines to false during a test to disable goroutine debugging
+// results in race detector complaints when a test leaves goroutines running before
+// returning. Tests shouldn't do this, of course, but when they do it generally shows
+// up as infrequent, hard-to-debug flakes. (See #66519.)
+//
+// Disable goroutine debugging during individual tests with an atomic bool.
+// (Note that it's safe to enable/disable debugging mid-test, so the actual race condition
+// here is harmless.)
+var disableDebugGoroutines atomic.Bool
+
 type goroutineLock uint64
 
 func newGoroutineLock() goroutineLock {
-	if !DebugGoroutines {
+	if !DebugGoroutines || disableDebugGoroutines.Load() {
 		return 0
 	}
 	return goroutineLock(curGoroutineID())
 }
 
 func (g goroutineLock) check() {
-	if !DebugGoroutines {
+	if !DebugGoroutines || disableDebugGoroutines.Load() {
 		return
 	}
 	if curGoroutineID() != uint64(g) {
@@ -38,7 +49,7 @@ func (g goroutineLock) check() {
 }
 
 func (g goroutineLock) checkNotOn() {
-	if !DebugGoroutines {
+	if !DebugGoroutines || disableDebugGoroutines.Load() {
 		return
 	}
 	if curGoroutineID() == uint64(g) {
diff --git a/http2/server_test.go b/http2/server_test.go
index af1ebe04..71287d1e 100644
--- a/http2/server_test.go
+++ b/http2/server_test.go
@@ -3520,9 +3520,10 @@ func testServerContentLengthCanBeDisabled(t testing.TB) {
 }
 
 func disableGoroutineTracking(t testing.TB) {
-	old := DebugGoroutines
-	DebugGoroutines = false
-	t.Cleanup(func() { DebugGoroutines = old })
+	disableDebugGoroutines.Store(true)
+	t.Cleanup(func() {
+		disableDebugGoroutines.Store(false)
+	})
 }
 
 func BenchmarkServer_GetRequest(b *testing.B) {