[Lldb-commits] [PATCH] D157654: [lldb] Fix data race in PipePosix

[Augusto Noronha via Phabricator via lldb-commits]

augusto2112 added inline comments.


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Comment at: lldb/source/Host/posix/PipePosix.cpp:69
   PipeBase::operator=(std::move(pipe_posix));
-  m_fds[READ] = pipe_posix.ReleaseReadFileDescriptor();
-  m_fds[WRITE] = pipe_posix.ReleaseWriteFileDescriptor();
+  std::lock_guard<std::mutex> guard(m_lock);
+  m_fds[READ] = pipe_posix.ReleaseReadFileDescriptorUnlocked();
----------------
bulbazord wrote:
> I think this lock needs to be at the beginning. Scenario:
> 
> Thread 1 calls the move assign operator and performs the base move assign. Gets unscheduled before acquiring lock.
> Thread 2 calls the move assign operator and performs the base move assign. Acquires the lock, fills in `m_fds`, and returns.
> Thread 1 is scheduled again, grabs the lock, and fills in `m_fds`.
> `this` will have its `PipeBase` members filled in by the Thread 2 call while `m_fds` will be filled in by the Thread 1 call. Granted, one thread may be surprised that suddenly the thing didn't get moved in as expected, but at least `this` will be in a consistent state.
> 
> I think you also need to lock the mutex of `pipe_posix` at the same time. Imagine Thread 1 is trying to access something from `pipe_posix` while Thread 2 is trying to move it into another `PipePosix` object. (Not sure how likely this scenario is but I'd rather be safe than sorry).
> I think you also need to lock the mutex of pipe_posix at the same time. Imagine Thread 1 is trying to access something from pipe_posix while Thread 2 is trying to move it into another PipePosix object. (Not sure how likely this scenario is but I'd rather be safe than sorry).

Yeah I thought about this too, since `pipe_posix` is an rvalue reference I was thinking this shouldn't be necessary, but you're right, I'll lock it anyway.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157654/new/

https://reviews.llvm.org/D157654