From 9556a0c6da5b5e8186477711c2003a07e5831fda Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Wed, 8 Oct 2025 07:50:56 -0700
Subject: [PATCH] control/ts2021: fix data race during concurrent Close and
 conn ending

Fixes tailscale/corp#33125

Change-Id: I9911f5059d5ebe42ecf7db9becb2326cca240765
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
---
 control/ts2021/client.go | 1 +
 1 file changed, 1 insertion(+)

diff --git a/control/ts2021/client.go b/control/ts2021/client.go
index e0b82b89c..ca10b1d1b 100644
--- a/control/ts2021/client.go
+++ b/control/ts2021/client.go
@@ -180,6 +180,7 @@ func (nc *Client) Close() error {
 	nc.mu.Lock()
 	live := nc.connPool
 	nc.closed = true
+	nc.connPool = nil // stop noteConnClosed from mutating it as we loop over it (in live) below
 	nc.mu.Unlock()
 
 	for _, c := range live {