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GeezerVison is showing github.com — gh-101696: Make sure immutable types have a valid version tag by erlend-aasland · Pull Request #101742 · python/cpython

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@erlend-aasland

@erlend-aasland erlend-aasland commented Feb 9, 2023 •
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Reverts #101697

  • Issue: _PyStaticType_Dealloc does not invalidate type version tag #101696

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@erlend-aasland
pythongh-101696: Make sure immutable types have a valid version tag
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@bedevere-bot bedevere-bot added the awaiting core review label Feb 9, 2023
@bedevere-bot bedevere-bot mentioned this pull request Feb 9, 2023
_PyStaticType_Dealloc does not invalidate type version tag #101696
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@erlend-aasland

erlend-aasland commented Feb 9, 2023

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cc. @markshannon @kumaraditya303
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@erlend-aasland
erlend-aasland requested a review from kumaraditya303 February 9, 2023 14:23
@erlend-aasland erlend-aasland added the skip news label Feb 9, 2023
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erlend-aasland commented Feb 9, 2023

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I guess we can skip NEWS, as this is strictly internal.
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@erlend-aasland
erlend-aasland marked this pull request as ready for review February 9, 2023 17:13
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erlend-aasland requested a review from markshannon as a code owner February 9, 2023 17:13
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erlend-aasland requested review from ericsnowcurrently and removed request for markshannon February 9, 2023 17:14
@kumaraditya303

kumaraditya303 commented Feb 9, 2023

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I'll review this by tomorrow.
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ericsnowcurrently
ericsnowcurrently requested changes Feb 9, 2023
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LGTM

FWIW, it would be nice if there were a test that covered the original problem from gh-101696 (i.e. fail without the fix and pass with it), whether by crashing or some other means. Would you mind adding something like that in this PR.

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Comment thread Objects/typeobject.c
Comment on lines +232 to +237
if (_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
CHECK(type->tp_version_tag != 0);
}
else {
CHECK(type->tp_version_tag == 0);
}

@ericsnowcurrently ericsnowcurrently Feb 9, 2023

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This check is worth adding, regardless of the rest of this PR, right?

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@erlend-aasland erlend-aasland Feb 9, 2023

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Yes

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Comment thread Objects/typeobject.c
Comment on lines +6979 to +6983
/* All immutable types must have a static valid version tag */
if (type->tp_flags & Py_TPFLAGS_IMMUTABLETYPE) {
type->tp_version_tag = next_version_tag++;
type->tp_flags |= Py_TPFLAGS_VALID_VERSION_TAG;
}

@ericsnowcurrently ericsnowcurrently Feb 9, 2023

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tl;dr I'm on board with this.

As I mentioned in gh-101696, this is good as it covers non-builtin static types (AKA non-_Py_TPFLAGS_STATIC_BUILTIN), e.g. in community extension modules. 1 (The switch to Py_TPFLAGS_IMMUTABLETYPE seems fine.)

FWIW, the already merged fix may fit a little better with the vague idea (in my head) that we should be special-casing static types in the runtime as little as possible (or otherwise in more explicit ways, like the dedicated _PyStaticType_Dealloc()). In that spirit, rather than modifying PyType_Ready(), I was going to suggest we could find a way to apply _PyStaticType_Dealloc() to all static types, not just the builtin ones, which might be a good idea regardless. However, that feels like overkill for fixing this issue. Plus, we're already special-casing static types here in PyType_Ready(). (Perhaps my mental model is misaligned...)

Bottom line: dropping the original fix and adding the fix you have here is worth it since it handles non-builtin static types too.

Footnotes

  1. One could argue that non-builtin (non-core) static types should be discouraged (basically, they already are) and we shouldn't bother adding extra maintenance burden--however small--to accommodate them. However, that's not where the community is at nor will be for a long time and there's no reason to be so hard-line about it, especially in a case like this where the additional maintenance burden is essentially zero. ↩

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@erlend-aasland erlend-aasland Feb 9, 2023

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Note that this PR does not special-case static types; the condition is for immutable types.

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@bedevere-bot bedevere-bot added awaiting changes and removed awaiting core review labels Feb 9, 2023
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bedevere-bot commented Feb 9, 2023

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When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

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@erlend-aasland

erlend-aasland commented Feb 9, 2023 •
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it would be nice if there were a test that covered the original problem from gh-101696 (i.e. fail without the fix and pass with it), whether by crashing or some other means. Would you mind adding something like that in this PR.

The original problem was uncovered by test_finalize_structseq in test_embed in gh-101304. Without Kumar's fix (d9de079), that particular test segfaulted. With Kumar's fix applied, the test passed; with Kumar's fix reverted and this PR applied, the test also passes.

I could of course try to add a more deterministic test. I'm not quite sure how to provoke that ATM, but I can look into it.
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@erlend-aasland erlend-aasland added the DO-NOT-MERGE label Feb 10, 2023
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erlend-aasland commented Feb 10, 2023

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Closing, as per discussion on the issue.
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@erlend-aasland erlend-aasland closed this Feb 10, 2023
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erlend-aasland deleted the versiontag branch February 10, 2023 17:45
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