René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Race between `_PyParkingLot_Park` and `_PyParkingLot_UnparkAll` when handling interrupts","articleBody":"# Bug report\n\n### Bug description:\n\nThere is a potential race when `_PyParkingLot_UnparkAll` is executing in one thread and another thread is unblocked because of an interrupt in `_PyParkingLot_Park`. Consider the following scenario:\n\n1. Thread T0 is [blocked](https://github.com/python/cpython/blob/f35c7c070ca6b49c5d6a97be34e6c02f828f5873/Python/parking_lot.c#L303) in `_PyParkingLot_Park` on address `A`.\n2. Thread T1 executes `_PyParkingLot_UnparkAll` on address `A`. It finds the `wait_entry` for `T0` and [unlinks](https://github.com/python/cpython/blob/f35c7c070ca6b49c5d6a97be34e6c02f828f5873/Python/parking_lot.c#L369) its list node.\n3. Immediately after (2), T0 is woken up due to an interrupt. It then segfaults trying to [unlink](https://github.com/python/cpython/blob/f35c7c070ca6b49c5d6a97be34e6c02f828f5873/Python/parking_lot.c#L320) the node that was previously unlinked in (2).\n\nI haven't attempted to write a minimal repro for this. It occurs reliably on MacOS on [this PR](https://github.com/python/cpython/pull/114839) when running `./python.exe -m test test_asyncio.test_events --match test_get_event_loop_new_process`.\n\n\n### CPython versions tested on:\n\nCPython main branch\n\n### Operating systems tested on:\n\nmacOS\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-114945\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/mpage","@type":"Person","name":"mpage"},"datePublished":"2024-02-03T01:44:29.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/114944/cpython/issues/114944"}