From d3297f0734ae81d9148ce068f33efeef5c155c97 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Wed, 7 Mar 2018 10:52:30 +0700
Subject: [PATCH] fix race condition when setting up TLS sessions in the server

---
 server.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/server.go b/server.go
index 499e52e4d..7a19afcb5 100644
--- a/server.go
+++ b/server.go
@@ -140,10 +140,11 @@ func (s *server) setupTLS() error {
 			case tlsSession := <-sessionChan:
 				connID := tlsSession.connID
 				sess := tlsSession.sess
+				s.sessionsMutex.Lock()
 				if _, ok := s.sessions[connID]; ok { // drop this session if it already exists
+					s.sessionsMutex.Unlock()
 					continue
 				}
-				s.sessionsMutex.Lock()
 				s.sessions[connID] = sess
 				s.sessionsMutex.Unlock()
 				s.runHandshakeAndSession(sess, connID)