[Lldb-commits] [lldb] [lldb-dap] Fix mutex acquisition order for modules event. (PR #163821)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Ebuka Ezike (da-viper)

<details>
<summary>Changes</summary>

The modules event requires the `APIMutex` to create the module load address. this may happen at the same time the `module request` is handled.

The modules request also requires the `APIMutex` and the `modules_mutex, set the order to acquire the mutexes.

---
Full diff: https://github.com/llvm/llvm-project/pull/163821.diff


1 Files Affected:

- (modified) lldb/tools/lldb-dap/DAP.cpp (+6-1) 


``````````diff
diff --git a/lldb/tools/lldb-dap/DAP.cpp b/lldb/tools/lldb-dap/DAP.cpp
index f76656e98ca01..003b55fa31610 100644
--- a/lldb/tools/lldb-dap/DAP.cpp
+++ b/lldb/tools/lldb-dap/DAP.cpp
@@ -1437,7 +1437,12 @@ void DAP::EventThread() {
           const bool remove_module =
               event_mask & lldb::SBTarget::eBroadcastBitModulesUnloaded;
 
-          std::lock_guard<std::mutex> guard(modules_mutex);
+          // NOTE: Both mutexes must be acquired (API mutex first, then modules
+          // mutex) to prevent deadlock when handling `modules_request`, which
+          // also requires both locks.
+          lldb::SBMutex api_mutex = GetAPIMutex();
+          std::lock_guard api_guard(api_mutex);
+          std::lock_guard modules_guard(modules_mutex);
           for (uint32_t i = 0; i < num_modules; ++i) {
             lldb::SBModule module =
                 lldb::SBTarget::GetModuleAtIndexFromEvent(i, event);

``````````

</details>


https://github.com/llvm/llvm-project/pull/163821