[Lldb-commits] [PATCH] D157347: [lldb] Fix data race in ConnectionFileDescriptor

[Jonas Devlieghere via Phabricator via lldb-commits]

JDevlieghere created this revision.
JDevlieghere added reviewers: bulbazord, augusto2112.
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JDevlieghere requested review of this revision.

TSan reports the following data race:

  Write of size 4 at 0x000109e0b160 by thread T2 (mutexes: write M0, write M1):
    #0 lldb_private::NativeFile::Close() File.cpp:329 (liblldb.18.0.0git.dylib:arm64+0x58dac0)
    #1 lldb_private::ConnectionFileDescriptor::Disconnect(lldb_private::Status*) ConnectionFileDescriptorPosix.cpp:232 (liblldb.18.0.0git.dylib:arm64+0x5bad6c)
    #2 lldb_private::Communication::Disconnect(lldb_private::Status*) Communication.cpp:61 (liblldb.18.0.0git.dylib:arm64+0x451f04)
    #3 lldb_private::process_gdb_remote::ProcessGDBRemote::DidExit() ProcessGDBRemote.cpp:1164 (liblldb.18.0.0git.dylib:arm64+0xadfd80)
    #4 lldb_private::Process::SetExitStatus(int, char const*) Process.cpp:1097 (liblldb.18.0.0git.dylib:arm64+0x6ed338)
    #5 lldb_private::process_gdb_remote::ProcessGDBRemote::MonitorDebugserverProcess(std::__1::weak_ptr<lldb_private::process_gdb_remote::ProcessGDBRemote>, unsigned long long, int, int) ProcessGDBRemote.cpp:3387 (liblldb.18.0.0git.dylib:arm64+0xae9464)
  
  Previous read of size 4 at 0x000109e0b160 by main thread (mutexes: write M2):
    #0 lldb_private::NativeFile::IsValid() const File.h:393 (liblldb.18.0.0git.dylib:arm64+0x590830)
    #1 lldb_private::ConnectionFileDescriptor::IsConnected() const ConnectionFileDescriptorPosix.cpp:121 (liblldb.18.0.0git.dylib:arm64+0x5b8ab4)
    #2 lldb_private::Communication::IsConnected() const Communication.cpp:79 (liblldb.18.0.0git.dylib:arm64+0x451fcc)
    #3 lldb_private::process_gdb_remote::GDBRemoteCommunication::WaitForPacketNoLock(StringExtractorGDBRemote&, lldb_private::Timeout<std::__1::ratio<1l, 1000000l>>, bool) GDBRemoteCommunication.cpp:256 (liblldb.18.0.0git.dylib:arm64+0xaac060)
    #4 lldb_private::process_gdb_remote::GDBRemoteCommunication::WaitForPacketNoLock(StringExtractorGDBRemote&, lldb_private::Timeout<std::__1::ratio<1l, 1000000l>>, bool) GDBRemoteCommunication.cpp:244 (liblldb.18.0.0git.dylib:arm64+0xaabe78)
    #5 lldb_private::process_gdb_remote::GDBRemoteClientBase::SendPacketAndWaitForResponseNoLock(llvm::StringRef, StringExtractorGDBRemote&) GDBRemoteClientBase.cpp:246 (liblldb.18.0.0git.dylib:arm64+0xaaa184)

The problem is that in `WaitForPacketNoLock`'s run loop, it checks that the connection is still connected. This races with the `ConnectionFileDescriptor` disconnecting. Most (but not all) access to the `IOObject` in `ConnectionFileDescriptorPosix` is already gated by the mutex. This patch just protects `IsConnected` in the same way.


https://reviews.llvm.org/D157347

Files:
  lldb/include/lldb/Host/posix/ConnectionFileDescriptorPosix.h
  lldb/source/Host/posix/ConnectionFileDescriptorPosix.cpp


Index: lldb/source/Host/posix/ConnectionFileDescriptorPosix.cpp
===================================================================
--- lldb/source/Host/posix/ConnectionFileDescriptorPosix.cpp
+++ lldb/source/Host/posix/ConnectionFileDescriptorPosix.cpp
@@ -118,6 +118,7 @@
 }
 
 bool ConnectionFileDescriptor::IsConnected() const {
+  std::lock_guard<std::recursive_mutex> guard(m_mutex);
   return m_io_sp && m_io_sp->IsValid();
 }
 
Index: lldb/include/lldb/Host/posix/ConnectionFileDescriptorPosix.h
===================================================================
--- lldb/include/lldb/Host/posix/ConnectionFileDescriptorPosix.h
+++ lldb/include/lldb/Host/posix/ConnectionFileDescriptorPosix.h
@@ -131,7 +131,7 @@
   lldb::IOObjectSP m_io_sp;
 
   Pipe m_pipe;
-  std::recursive_mutex m_mutex;
+  mutable std::recursive_mutex m_mutex;
   std::atomic<bool> m_shutting_down; // This marks that we are shutting down so
                                      // if we get woken up from
   // BytesAvailable to disconnect, we won't try to read again.


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