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Title: Prevent array.fromfile reentrancy deadlock in append conversion by Copilot · Pull Request #6576 · RustPython/RustPython · GitHub

Open Graph Title: Prevent array.fromfile reentrancy deadlock in append conversion by Copilot · Pull Request #6576 · RustPython/RustPython

X Title: Prevent array.fromfile reentrancy deadlock in append conversion by Copilot · Pull Request #6576 · RustPython/RustPython

Description: array.fromfile could deadlock when __index__ invoked during element conversion performed a nested append on the same array. Append conversion before locking: Convert elements (capturing array kind) prior to acquiring the write lock, then push with a runtime invariant check to avoid reentrant deadlocks. Stronger invariants: Added typed helpers (ArrayType/ArrayElementValue) with assertive mismatch diagnostics to catch unexpected kind/value divergence. Regression coverage: Extended extra_tests/snippets/stdlib_array.py with a reentrancy scenario where fromfile triggers __index__ that re-appends to the same array. Example: import array a = array.array("b") class X: def __index__(self): a.append(0) # reenters append while fromfile is mid-conversion return 0 class R: def read(self, n): a.append(X()) return b"\0" * n a.fromfile(R(), 1) # no deadlock; contents now [0, 0, 0] Original prompt This section details on the original issue you should resolve Deadlock when array.fromfile re-enters append via __index__ ### What happened? array.fromfile calls the user-provided f.read(), and that callback can append objects to the same array while it is being resized. The append path grabs the array's write lock before converting the element, then calls the object's __index__. If __index__ performs another array.append (as in the PoC), the second append blocks forever on the already-held PyRwLock, causing a deadlock instead of raising an error. Proof of Concept: import array a = array.array("b") class X: def __index__(self): a.append(0) return 0 class R: def read(self, n): a.append(X()) return b"\0" * n a.fromfile(R(), 1) Affected Versions RustPython Version Status Exit Code Python 3.13.0alpha (heads/main-dirty:21300f689, Dec 13 2025, 22:16:49) [RustPython 0.4.0 with rustc 1.90.0-nightly (11ad40bb8 2025-06-28)] Deadlock 124 Vulnerable Code #[pymethod] fn fromfile(&self, f: PyObjectRef, n: isize, vm: &VirtualMachine) -> PyResult<()> { let b = vm.call_method(&f, "read", (n_bytes,))?; // user f.read runs arbitrary code while the array can still be mutated ... } #[pymethod] fn append(zelf: &Py, x: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> { zelf.try_resizable(vm)?.push(x, vm) // takes a non-reentrant PyRwLock write guard before converting x } impl ArrayElement for i8 { fn try_into_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult { obj.try_index(vm)?.try_to_primitive(vm) // invokes __index__ while the write lock is held; reentrant array.append inside __index__ deadlocks } } impl BufferResizeGuard for PyArray { fn try_resizable_opt(&self) -> Option> { let w = self.write(); // second append blocks here waiting on the same PyRwLock, hanging the interpreter (self.exports.load(atomic::Ordering::SeqCst) == 0).then_some(w) } } Rust Output Program hangs forever CPython Output (No output) Add the code to stdlib_array.py and fix the problem. Comments on the Issue (you are @copilot in this section) Fixes #6549 💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

Open Graph Description: array.fromfile could deadlock when __index__ invoked during element conversion performed a nested append on the same array. Append conversion before locking: Convert elements (capturing array kind...

X Description: array.fromfile could deadlock when __index__ invoked during element conversion performed a nested append on the same array. Append conversion before locking: Convert elements (capturing array kind...

Opengraph URL: https://github.com/RustPython/RustPython/pull/6576

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