[Lldb-commits] [lldb] Don't hold the Target's ModuleListLock over running LoadScriptingResourceInTarget (PR #138216)

[via lldb-commits]

https://github.com/jimingham created https://github.com/llvm/llvm-project/pull/138216

That calls an unknown amount of Python code, and can do quite a bit of work - especially if people do things like launch scripted processes in this script affordance.  Doing that while holding a major lock like the ModuleList lock is asking for trouble.

I tried to make a test that would actually stall without this, but I couldn't come up with anything that reliably failed.  You always have to get pretty unlucky.

>From 656fe559f84526fd3edc91b1c0d12fd56d838085 Mon Sep 17 00:00:00 2001
From: Jim Ingham <jingham at apple.com>
Date: Thu, 1 May 2025 16:27:37 -0700
Subject: [PATCH] Don't hold the Target's ModuleListLock over running
 LoadScriptingResourceInTarget. That calls an unknown amount of Python code,
 and can do quite a bit of work - especially if people do things like launch
 scripted processes in this script affordance.  Doing that while holding a
 major lock like the ModuleList lock is asking for trouble.

I tried to make a test that would actually stall without this, but I couldn't
come up with anything that reliably failed.  You always have to get pretty
unlucky.
---
 lldb/source/Core/ModuleList.cpp | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lldb/source/Core/ModuleList.cpp b/lldb/source/Core/ModuleList.cpp
index 6052cc151744d..9724039decf0d 100644
--- a/lldb/source/Core/ModuleList.cpp
+++ b/lldb/source/Core/ModuleList.cpp
@@ -1046,8 +1046,14 @@ bool ModuleList::LoadScriptingResourcesInTarget(Target *target,
                                                 bool continue_on_error) {
   if (!target)
     return false;
-  std::lock_guard<std::recursive_mutex> guard(m_modules_mutex);
-  for (auto module : m_modules) {
+  m_modules_mutex.lock();
+  // Don't hold the module list mutex while loading the scripting resources,
+  // The initializer might do any amount of work, and having that happen while
+  // the module list is held is asking for A/B locking problems.
+  const ModuleList tmp_module_list(*this);
+  m_modules_mutex.unlock();
+  
+  for (auto module : tmp_module_list.ModulesNoLocking()) {
     if (module) {
       Status error;
       if (!module->LoadScriptingResourceInTarget(target, error,