From d7cf0cfdb4427b2d2bcd13ad15dcacfae056cd9e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Claus=20Lensb=C3=B8l?= <claus@tailscale.com>
Date: Fri, 21 Nov 2025 14:49:37 -0500
Subject: [PATCH] wgengine/userspace: run link change subscribers in eventqueue
 (#18024)
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Updates #17996

Signed-off-by: Claus Lensbøl <claus@tailscale.com>
(cherry picked from commit e7f5ca1d5ed23d2e3ae2fc9711b25dbd936bdb68)
---
 wgengine/userspace.go | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/wgengine/userspace.go b/wgengine/userspace.go
index 8856a3eaf..af26f72f8 100644
--- a/wgengine/userspace.go
+++ b/wgengine/userspace.go
@@ -50,6 +50,7 @@ import (
 	"tailscale.com/util/checkchange"
 	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/eventbus"
+	"tailscale.com/util/execqueue"
 	"tailscale.com/util/mak"
 	"tailscale.com/util/set"
 	"tailscale.com/util/testenv"
@@ -97,6 +98,8 @@ type userspaceEngine struct {
 	eventBus    *eventbus.Bus
 	eventClient *eventbus.Client
 
+	linkChangeQueue execqueue.ExecQueue
+
 	logf           logger.Logf
 	wgLogger       *wglog.Logger // a wireguard-go logging wrapper
 	reqCh          chan struct{}
@@ -543,7 +546,7 @@ func NewUserspaceEngine(logf logger.Logf, conf Config) (_ Engine, reterr error)
 		if f, ok := feature.HookProxyInvalidateCache.GetOk(); ok {
 			f()
 		}
-		e.linkChange(&cd)
+		e.linkChangeQueue.Add(func() { e.linkChange(&cd) })
 	})
 	e.eventClient = ec
 	e.logf("Engine created.")
@@ -1258,6 +1261,9 @@ func (e *userspaceEngine) RequestStatus() {
 
 func (e *userspaceEngine) Close() {
 	e.eventClient.Close()
+	// TODO(cmol): Should we wait for it too?
+	// Same question raised in appconnector.go.
+	e.linkChangeQueue.Shutdown()
 	e.mu.Lock()
 	if e.closing {
 		e.mu.Unlock()