From 0285e1d5fb2b06cd4003ab3a7c1037caa091a85e Mon Sep 17 00:00:00 2001
From: Jordan Whited <jordan@tailscale.com>
Date: Fri, 14 Nov 2025 10:22:58 -0800
Subject: [PATCH] feature/relayserver: fix Shutdown() deadlock (#17898)

Updates #17894

Signed-off-by: Jordan Whited <jordan@tailscale.com>
---
 feature/relayserver/relayserver.go | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/feature/relayserver/relayserver.go b/feature/relayserver/relayserver.go
index 2646a0cbf..868d5f61a 100644
--- a/feature/relayserver/relayserver.go
+++ b/feature/relayserver/relayserver.go
@@ -246,10 +246,13 @@ func (e *extension) stopRelayServerLocked() {
 
 // Shutdown implements [ipnlocal.Extension].
 func (e *extension) Shutdown() error {
+	// [extension.mu] must not be held when closing the [eventbus.Client]. Close
+	// blocks until all [eventbus.SubscribeFunc]'s have returned, and the ones
+	// used in this package also acquire [extension.mu]. See #17894.
+	e.ec.Close()
 	e.mu.Lock()
 	defer e.mu.Unlock()
 	e.shutdown = true
-	e.ec.Close()
 	e.stopRelayServerLocked()
 	return nil
 }