[lldb] Fix data race in ThreadList

ThreadSanitizer reports the following issue: ``` Write of size 8 at 0x00010a70abb0 by thread T3 (mutexes: write M0): #0 lldb_private::ThreadList::Update(lldb_private::ThreadList&) ThreadList.cpp:741 (liblldb.18.0.0git.dylib:arm64+0x5dedf4) (BuildId: 9bced2aafa373580ae9d750d9cf79a8f32000000200000000100000000000e00) #1 lldb_private::Process::UpdateThreadListIfNeeded() Process.cpp:1212 (liblldb.18.0.0git.dylib:arm64+0x53bbec) (BuildId: 9bced2aafa373580ae9d750d9cf79a8f32000000200000000100000000000e00) Previous read of size 8 at 0x00010a70abb0 by main thread (mutexes: write M1): #0 lldb_private::ThreadList::GetMutex() const ThreadList.cpp:785 (liblldb.18.0.0git.dylib:arm64+0x5df138) (BuildId: 9bced2aafa373580ae9d750d9cf79a8f32000000200000000100000000000e00) #1 lldb_private::ThreadList::DidResume() ThreadList.cpp:656 (liblldb.18.0.0git.dylib:arm64+0x5de5c0) (BuildId: 9bced2aafa373580ae9d750d9cf79a8f32000000200000000100000000000e00) #2 lldb_private::Process::PrivateResume() Process.cpp:3130 (liblldb.18.0.0git.dylib:arm64+0x53cd7c) (BuildId: 9bced2aafa373580ae9d750d9cf79a8f32000000200000000100000000000e00) ``` Fix this by only using the mutex in ThreadList and removing the one in process entirely. Differential Revision: https://reviews.llvm.org/D158034
llvm · Aug 18, 2023 · bb90063 · bb90063
1 parent 9c08e76
commit bb90063
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Showing 5 changed files with 5 additions and 11 deletions.
diff --git a/lldb/include/lldb/Target/Process.h b/lldb/include/lldb/Target/Process.h
@@ -2970,7 +2970,6 @@ void PruneThreadPlans();
   std::string m_exit_string; ///< A textual description of why a process exited.
   std::mutex m_exit_status_mutex; ///< Mutex so m_exit_status m_exit_string can
                                   ///be safely accessed from multiple threads
-  std::recursive_mutex m_thread_mutex;
   ThreadList m_thread_list_real; ///< The threads for this process as are known
                                  ///to the protocol we are debugging with
   ThreadList m_thread_list; ///< The threads for this process as the user will

diff --git a/lldb/include/lldb/Target/ThreadCollection.h b/lldb/include/lldb/Target/ThreadCollection.h
@@ -47,7 +47,7 @@ class ThreadCollection {
     return ThreadIterable(m_threads, GetMutex());
   }
 
-  virtual std::recursive_mutex &GetMutex() const { return m_mutex; }
+  std::recursive_mutex &GetMutex() const { return m_mutex; }
 
 protected:
   collection m_threads;

diff --git a/lldb/include/lldb/Target/ThreadList.h b/lldb/include/lldb/Target/ThreadList.h
@@ -133,8 +133,6 @@ class ThreadList : public ThreadCollection {
 
   void SetStopID(uint32_t stop_id);
 
-  std::recursive_mutex &GetMutex() const override;
-
   void Update(ThreadList &rhs);
 
 protected:

diff --git a/lldb/source/Target/Process.cpp b/lldb/source/Target/Process.cpp
@@ -435,7 +435,7 @@ Process::Process(lldb::TargetSP target_sp, ListenerSP listener_sp,
           Listener::MakeListener("lldb.process.internal_state_listener")),
       m_mod_id(), m_process_unique_id(0), m_thread_index_id(0),
       m_thread_id_to_index_id_map(), m_exit_status(-1), m_exit_string(),
-      m_exit_status_mutex(), m_thread_mutex(), m_thread_list_real(this),
+      m_exit_status_mutex(), m_thread_list_real(this),
       m_thread_list(this), m_thread_plans(*this), m_extended_thread_list(this),
       m_extended_thread_stop_id(0), m_queue_list(this), m_queue_list_stop_id(0),
       m_notifications(), m_image_tokens(),
@@ -2456,7 +2456,7 @@ Process::WaitForProcessStopPrivate(EventSP &event_sp,
 }
 
 void Process::LoadOperatingSystemPlugin(bool flush) {
-  std::lock_guard<std::recursive_mutex> guard(m_thread_mutex);
+  std::lock_guard<std::recursive_mutex> guard(GetThreadList().GetMutex());
   if (flush)
     m_thread_list.Clear();
   m_os_up.reset(OperatingSystem::FindPlugin(this, nullptr));

diff --git a/lldb/source/Target/ThreadList.cpp b/lldb/source/Target/ThreadList.cpp
@@ -736,7 +736,8 @@ void ThreadList::Update(ThreadList &rhs) {
   if (this != &rhs) {
     // Lock both mutexes to make sure neither side changes anyone on us while
     // the assignment occurs
-    std::scoped_lock<std::recursive_mutex, std::recursive_mutex> guard(GetMutex(), rhs.GetMutex());
+    std::scoped_lock<std::recursive_mutex, std::recursive_mutex> guard(
+        GetMutex(), rhs.GetMutex());
 
     m_process = rhs.m_process;
     m_stop_id = rhs.m_stop_id;
@@ -781,10 +782,6 @@ void ThreadList::Flush() {
     (*pos)->Flush();
 }
 
-std::recursive_mutex &ThreadList::GetMutex() const {
-  return m_process->m_thread_mutex;
-}
-
 ThreadList::ExpressionExecutionThreadPusher::ExpressionExecutionThreadPusher(
     lldb::ThreadSP thread_sp)
     : m_thread_list(nullptr), m_tid(LLDB_INVALID_THREAD_ID) {