runtime: define lock ranking between weak pointers and synctest

Fixes #73817

Change-Id: I0101bdc797237b4c7eb58b414c71b009b0b44447
Reviewed-on: https://go-review.googlesource.com/c/go/+/675176
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Damien Neil <dneil@google.com>

Author: neild

src/internal/synctest/synctest_test.go

@@ -9,11 +9,13 @@ import (
 	"internal/synctest"
 	"iter"
 	"reflect"
+	"runtime"
 	"slices"
 	"strconv"
 	"sync"
 	"testing"
 	"time"
+	"weak"
 )
 
 func TestNow(t *testing.T) {
@@ -625,6 +627,17 @@ func TestHappensBefore(t *testing.T) {
 	}
 }
 
+// https://go.dev/issue/73817
+func TestWeak(t *testing.T) {
+	synctest.Run(func() {
+		for range 100 {
+			runtime.GC()
+			b := make([]byte, 1024)
+			weak.Make(&b)
+		}
+	})
+}
+
 func wantPanic(t *testing.T, want string) {
 	if e := recover(); e != nil {
 		if got := fmt.Sprint(e); got != want {

src/runtime/lockrank.go

@@ -99,7 +99,15 @@ NONE
 < reflectOffs;
 
 # Synctest
-hchan, root, timers, timer, notifyList, reflectOffs < synctest;
+hchan,
+  notifyList,
+  reflectOffs,
+  root,
+  strongFromWeakQueue,
+  sweepWaiters,
+  timer,
+  timers
+< synctest;
 
 # User arena state
 NONE < userArenaState;