[lldb] Fixed lldb-server crash (TestLogHandler was not thread safe)

[slydiman]

Host::LaunchProcess() requires to SetMonitorProcessCallback. This callback is called from the child process monitor thread. We cannot control this thread anyway. lldb-server may crash if there is a logging around this callback because TestLogHandler is not thread safe. I faced this issue debugging 100 simultaneous child processes. Note StreamLogHandler::Emit() in lldb/source/Utility/Log.cpp already contains the similar mutex.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Dmitry Vasilyev (slydiman)

Changes

Host::LaunchProcess() requires to SetMonitorProcessCallback. This callback is called from the child process monitor thread. We cannot control this thread anyway. lldb-server may crash if there is a logging around this callback because TestLogHandler is not thread safe. I faced this issue debugging 100 simultaneous child processes. Note StreamLogHandler::Emit() in lldb/source/Utility/Log.cpp already contains the similar mutex.

---

Full diff: https://github.com/llvm/llvm-project/pull/101326.diff

1 Files Affected:

• (modified) lldb/tools/lldb-server/LLDBServerUtilities.cpp (+2)

diff --git a/lldb/tools/lldb-server/LLDBServerUtilities.cpp b/lldb/tools/lldb-server/LLDBServerUtilities.cpp
index c3a8df19e969e..5facfbf3105e9 100644
--- a/lldb/tools/lldb-server/LLDBServerUtilities.cpp
+++ b/lldb/tools/lldb-server/LLDBServerUtilities.cpp
@@ -27,11 +27,13 @@ class TestLogHandler : public LogHandler {
       : m_stream_sp(stream_sp) {}
 
   void Emit(llvm::StringRef message) override {
+    std::lock_guard<std::mutex> guard(m_mutex);
     (*m_stream_sp) << message;
     m_stream_sp->flush();
   }
 
 private:
+  std::mutex m_mutex;
   std::shared_ptr<raw_ostream> m_stream_sp;
 };
 

[labath]

This makes sense, though it would probably be even better to just use the real StreamLogHandler class. I think all that's needed would be to add a new constructor to it.