[all-commits] [llvm/llvm-project] bab217: [mlir][python] Fix segfault at interpreter shutdow...

[Maksim Levental via All-commits]

  Branch: refs/heads/users/makslevental/fix-PyThreadContextEntry-sigsegv
  Home:   https://github.com/llvm/llvm-project
  Commit: bab217b338ae7ed2d5d43a735b75c3c667a36e6b
      https://github.com/llvm/llvm-project/commit/bab217b338ae7ed2d5d43a735b75c3c667a36e6b
  Author: makslevental <m_levental at apple.com>
  Date:   2026-06-14 (Sun, 14 Jun 2026)

  Changed paths:
    M mlir/lib/Bindings/Python/IRCore.cpp
    A mlir/test/python/context_shutdown.py

  Log Message:
  -----------
  [mlir][python] Fix segfault at interpreter shutdown with entered contexts

The thread-local context stack (`PyThreadContextEntry::getStack()`)
holds `nb::object` references to Python Context, Location, and
InsertionPoint objects. When a Context is entered via `__enter__` but
never exited before the interpreter shuts down, these references
cause a segfault during process teardown.

The crash sequence:
1. User calls `ctx.__enter__()`, pushing a frame onto the
   `static thread_local vector<PyThreadContextEntry>`.
2. The script ends; CPython runs `Py_FinalizeEx()` which tears down
   the interpreter (clears modules, destroys remaining objects).
3. `main()` returns.
4. The C runtime destroys static/thread_local storage. On the main
   thread, thread_local variables have the same destruction timing
   as static storage — they are destroyed *after* main() returns.
5. The vector destructor runs, and each `PyThreadContextEntry`'s
   `nb::object` members call `Py_DECREF` — but the interpreter is
   already dead. This dereferences freed memory → SIGSEGV.

The fix registers a Python `atexit` handler that clears the
thread-local stack. Python's atexit handlers run *before*
`Py_FinalizeEx()`, while the interpreter is still fully alive,
so the `nb::object` decrefs execute safely.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply at anthropic.com>



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