[Lldb-commits] [lldb] [lldb][Windows] Lock the thread list when lldb-server adds a thread (PR #226974)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Charles Zablit (charles-zablit)

<details>
<summary>Changes</summary>

`NativeProcessProtocol::Threads()` returns a `LockingAdaptedIterable` that holds `m_threads_mutex` for the lifetime of the iteration, so callers may hold references into `m_threads` across the loop body. On Windows, this is only done when removing threads:

```
  // OnCreateThread
  m_threads.push_back(std::move(thread));
...
  // OnExitThread
  std::lock_guard<std::recursive_mutex> guard(m_threads_mutex);
  llvm::erase_if(m_threads, ...);
```

`m_threads` is a `std::vector<std::unique_ptr<NativeThreadProtocol>>`. When the debug-event thread appends and the vector reallocates, every reference held by a concurrent iteration on the main loop dangles. This takes lldb-server down with an access violation:

```
Exception Code: 0xC0000005
 #<!-- -->0 NativeThreadProtocol::GetID   NativeThreadProtocol.h:40
 #<!-- -->1 GetJSONThreadsInfo            GDBRemoteCommunicationServerLLGS.cpp:819
 #<!-- -->4 Handle_jThreadsInfo
 #<!-- -->8 GetPacketAndSendResponse
 #<!-- -->9 DataAvailableCallback         :1271
```

---
Full diff: https://github.com/llvm/llvm-project/pull/226974.diff


1 Files Affected:

- (modified) lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp (+2) 


``````````diff
diff --git a/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp b/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
index 849931eaec372..c24eebe82fd8d 100644
--- a/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
+++ b/lldb/source/Plugins/Process/Windows/Common/NativeProcessWindows.cpp
@@ -558,6 +558,7 @@ void NativeProcessWindows::OnDebuggerConnected(lldb::addr_t image_base) {
   }
 
   // The very first one shall always be the main thread.
+  std::lock_guard<std::recursive_mutex> guard(m_threads_mutex);
   assert(m_threads.empty());
   m_threads.push_back(std::make_unique<NativeThreadWindows>(
       *this, m_session_data->m_debugger->GetMainThread()));
@@ -783,6 +784,7 @@ void NativeProcessWindows::OnCreateThread(const HostThread &new_thread) {
     thread->SetStopReason(stop_info, "");
   }
 
+  std::lock_guard<std::recursive_mutex> guard(m_threads_mutex);
   m_threads.push_back(std::move(thread));
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/226974