wgengine/magicsock: unblock Conn.Synchronize on Conn.Close

bradfitz · bradfitz · commit 42ce5c88bed2 · 2025-11-11T00:41:47.000-08:00
I noticed a deadlock in a test in a in-development PR where during a shutdown storm of things (from a tsnet.Server.Close), LocalBackend was trying to call magicsock.Conn.Synchronize but the magicsock and/or eventbus was already shut down and no longer processing events. Updates tailscale#16369 Change-Id: I58b1f86c8959303c3fb46e2e3b7f38f6385036f1 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
@@ -665,7 +665,10 @@ func (c *Conn) Synchronize() {
 	}
 	sp := syncPoint(make(chan struct{}))
 	c.syncPub.Publish(sp)
-	sp.Wait()
+	select {
+	case <-sp:
+	case <-c.donec:
+	}
 }
 
 // NewConn creates a magic Conn listening on opts.Port.

Original file line number	Diff line number	Diff line change
`@@ -665,7 +665,10 @@ func (c *Conn) Synchronize() {`
`665`	`665`	`}`
`666`	`666`	`sp := syncPoint(make(chan struct{}))`
`667`	`667`	`c.syncPub.Publish(sp)`
`668`		`- sp.Wait()`
	`668`	`+ select {`
	`669`	`+ case <-sp:`
	`670`	`+ case <-c.donec:`
	`671`	`+ }`
`669`	`672`	`}`
`670`	`673`
`671`	`674`	`// NewConn creates a magic Conn listening on opts.Port.`