From 04d176425da9127ab726997d23e652197208edcf Mon Sep 17 00:00:00 2001
From: Koichi Sasada <ko1@atdot.net>
Date: Fri, 16 Sep 2022 15:35:53 +0900
Subject: [PATCH] fix timing issue

Before setting `@lock_file`, remote client can send stop request
to the parent process and it can cause data race issue.
---
 lib/debug/session.rb | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/debug/session.rb b/lib/debug/session.rb
index 303f3336d..c95edd57b 100644
--- a/lib/debug/session.rb
+++ b/lib/debug/session.rb
@@ -1893,9 +1893,11 @@ def multi_process!
 
     def after_fork child: true
       if child || !@lock_file
-        @m = Mutex.new
-        @lock_level = 0
-        @lock_file = open(@lock_tempfile.path, 'w')
+        @m = Mutex.new unless @m
+        @m.synchronize do
+          @lock_level = 0
+          @lock_file = open(@lock_tempfile.path, 'w')
+        end
       end
     end