[Lldb-commits] [lldb] bb90063 - [lldb] Fix data race in ThreadList

[Augusto Noronha via lldb-commits]

Author: Augusto Noronha
Date: 2023-08-18T16:53:26-07:00
New Revision: bb90063249707e3ae081bfbd8e3512566abb7df6

URL: https://github.com/llvm/llvm-project/commit/bb90063249707e3ae081bfbd8e3512566abb7df6
DIFF: https://github.com/llvm/llvm-project/commit/bb90063249707e3ae081bfbd8e3512566abb7df6.diff

LOG: [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

Added: 
    

Modified: 
    lldb/include/lldb/Target/Process.h
    lldb/include/lldb/Target/ThreadCollection.h
    lldb/include/lldb/Target/ThreadList.h
    lldb/source/Target/Process.cpp
    lldb/source/Target/ThreadList.cpp

Removed: 
    


################################################################################
diff  --git a/lldb/include/lldb/Target/Process.h b/lldb/include/lldb/Target/Process.h
index 2186eea7ef5054..2e1bce561526df 100644
--- 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
index 29f5103e7eec7c..dc7d8f13eee037 100644
--- 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
index 6af04f8ffc3767..8aaff6e4cba0d4 100644
--- 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
index fc08cce096103f..4a33d8980c2782 100644
--- 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
index 1ba0c435b993d3..fc6cbd48cf8653 100644
--- 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) {