[lldb-dap] Fix mutex acquisition order for modules event.

[da-viper]

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.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Ebuka Ezike (da-viper)

Changes

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 --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);

[JDevlieghere]

Thank you!

[ashgti]

LGTM!