GH-91636: Clear weakrefs created by finalizers. by nascheme · Pull Request #136401 · python/cpython

nascheme · 2025-07-08T00:33:15Z

Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have tp_clear called on them to Python-level code.

Note that this is part of the GH-136189 change, split out to make it easier for back-porting. This change is conceptually quite simple and is a candidate to backport to all older Python versions (this bug existed for a long time, perhaps in version 2.3). There is some duplicated code between handle_finalizers and clear_finalizers but I think it's simpler just to leave that duplication. In the "main" branch I'll clean that up.

Issue: Assertion failure when func_repr is called on an already tp_clear-ed object #91636

Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have `tp_clear` called on them to Python-level code.

nascheme · 2025-07-08T01:16:10Z

@colesbury In case you want to look at the free_threading_gc changes.

sergey-miryanov · 2025-07-08T05:40:23Z

Looks good to me.

Add a boolean flag to indicate that callbacks should be enabled. This allows the same function to be used before and after finalizer execution.

Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have `tp_clear` called on them to Python-level code.

sergey-miryanov · 2025-09-03T19:08:35Z

It seems that this is not backported to 3.14 and 3.13. Do we still a plan to backport it?
cc @nascheme, @Yhg1s, @hugovk

nascheme · 2025-09-04T10:05:25Z

Yeah, you are right. I think it would be good to backport this one.

hugovk · 2025-09-11T05:46:34Z

This bug had been around for a while, let's wait for 3.14.1 for the backport rather than do it during RC.

sergey-miryanov · 2025-11-25T19:38:08Z

@hugovk It's about 3.14.1 here. Should we backport this PR? I'm not sure about the process. Is it enough to add backport labels?

hugovk · 2025-11-26T21:02:50Z

@sergey-miryanov Yeah, please add the labels and Miss Islington will attempt backports. And then we can carefully review the backport PRs.

miss-islington-app · 2025-11-26T21:43:31Z

Thanks @nascheme for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

miss-islington-app · 2025-11-26T21:43:31Z

Thanks @nascheme for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have `tp_clear` called on them to Python-level code. (cherry picked from commit b6b99bf) Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>

miss-islington-app · 2025-11-26T21:43:38Z

Sorry, @nascheme, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker b6b99bf7f1edab77c485faf4e23da868f3a7b68c 3.13

bedevere-app · 2025-11-26T21:43:38Z

GH-141993 is a backport of this pull request to the 3.14 branch.

sergey-miryanov · 2025-11-26T21:45:02Z

I will look into manually backport this to 3.13
cc @Yhg1s @nascheme

…141993) GH-91636: Clear weakrefs created by finalizers. (GH-136401) Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have `tp_clear` called on them to Python-level code. (cherry picked from commit b6b99bf) Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>

…ythonGH-136401) (python#141993)" This reverts commit fed2af6.

…6401) (#141993)" (#142152)

serhiy-storchaka · 2025-12-26T09:58:30Z

Reminder about backporting to 3.13.

sergey-miryanov · 2026-01-23T14:49:13Z

Thanks for reminder. Sorry for the delay. Will work on backporting this weekends.

…H-136401) Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have `tp_clear` called on them to Python-level code. (cherry picked from commit b6b99bf) Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>

bedevere-app · 2026-01-24T19:17:52Z

GH-144214 is a backport of this pull request to the 3.13 branch.

miss-islington-app · 2026-02-03T20:00:34Z

Thanks @nascheme for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

miss-islington-app · 2026-02-03T20:00:36Z

Sorry, @nascheme, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker b6b99bf7f1edab77c485faf4e23da868f3a7b68c 3.14

…H-136401) Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have `tp_clear` called on them to Python-level code. (cherry picked from commit b6b99bf) Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>

bedevere-app · 2026-02-03T20:11:10Z

GH-144444 is a backport of this pull request to the 3.14 branch.

…144444) Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>

…H-144214) Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have `tp_clear` called on them to Python-level code. (cherry picked from commit b6b99bf) Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>

Clear weakrefs created by finalizers.
6a1b24b
Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have `tp_clear` called on them to Python-level code.

bedevere-appBot mentioned this pull request Jul 8, 2025
Assertion failure when func_repr is called on an already tp_clear-ed object #91636
Closed

nascheme added 3.13 bugs and security fixes 3.14 bugs and security fixes 3.15 pre-release feature fixes, bugs and security fixes labels Jul 8, 2025

nascheme marked this pull request as ready for review July 8, 2025 01:15

bedevere-appBot added the awaiting core review label Jul 8, 2025

nascheme requested review from colesbury and pablogsal July 8, 2025 01:15

colesbury reviewed Jul 8, 2025
View reviewed changes

Comment threadPython/gc_free_threading.c Outdated

Reduce code duplication.
412bc2a
Add a boolean flag to indicate that callbacks should be enabled. This allows the same function to be used before and after finalizer execution.

sergey-miryanov reviewed Jul 8, 2025
View reviewed changes

Comment threadPython/gc.c

nascheme merged commit b6b99bf into python:mainJul 8, 2025
40 checks passed

bedevere-appBot removed the awaiting core review label Jul 8, 2025

nascheme mentioned this pull request Jul 8, 2025
gh-135552: Make the GC clear weakrefs later #136189
Merged

sergey-miryanov added needs backport to 3.13 bugs and security fixes needs backport to 3.14 bugs and security fixes labels Nov 26, 2025

miss-islington-appBot assigned nascheme Nov 26, 2025

bedevere-appBot removed the needs backport to 3.14 bugs and security fixes label Nov 26, 2025

hugovk added a commit to hugovk/cpython that referenced this pull request Dec 1, 2025
Revert "[3.14]pythonGH-91636: Clear weakrefs created by finalizers. (p…
87b3635
…ythonGH-136401) (python#141993)" This reverts commit fed2af6.

hugovk added a commit that referenced this pull request Dec 1, 2025
[3.14] Revert "GH-91636: Clear weakrefs created by finalizers. (GH-13…
7642070
…6401) (#141993)" (#142152)

bedevere-appBot removed the needs backport to 3.13 bugs and security fixes label Jan 24, 2026

sergey-miryanov added the needs backport to 3.14 bugs and security fixes label Feb 3, 2026

bedevere-appBot removed the needs backport to 3.14 bugs and security fixes label Feb 3, 2026

hugovk pushed a commit that referenced this pull request Mar 12, 2026
[3.14]GH-91636: Clear weakrefs created by finalizers. (GH-136401) (#…
705e3ea
…144444) Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>

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