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GeezerVison is showing github.com — gh-158820: Add null checks to avoid segfaults with lazy imports at shutdown by brittanyrey · Pull Request #158821 · python/cpython

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@brittanyrey

@brittanyrey brittanyrey commented Oct 5, 2026 •
edited by bedevere-app Bot
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Additional finalizers can run after finalize_modules() has cleared the interpreter's lazy_modules set and lazy_pending_submodules dict. In the perfect storm, this can lead to a seg fault when accessing either container without checking if the object is still allocated.

  • Add null checks to call sites interacting with possibly cleared objects.
  • Adds tests repro-ing the issue
  • Issue: Segfault when a finalizer declares or resolves a lazy import during shutdown #158820

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brittanyrey added 2 commits October 4, 2026 18:41
@brittanyrey
Fix crash when a destructor uses lazy imports during shutdown
0b5852c 
Destructors can run after finalization has cleared the interpreter's
lazy_modules set and lazy_pending_submodules dict. Declaring or
resolving a lazy import from one of them passed NULL to PySet_Add(),
PySet_Discard() or the pending-submodules lookup.

Treat the bookkeeping as a no-op once the state is gone, as the other
readers of this state already do.
@brittanyrey
Remove comments on the lazy import state NULL checks
cc628a4
@brittanyrey
brittanyrey requested review from DinoV, FFY00, Yhg1s, brettcannon, ericsnowcurrently, kumaraditya303, ncoghlan, pablogsal and warsaw as code owners October 5, 2026 01:57
@bedevere-app bedevere-app Bot added the awaiting review label Oct 5, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Oct 5, 2026
Segfault when a finalizer declares or resolves a lazy import during shutdown #158820
Closed
@blurb-it
📜🤖 Added by blurb_it.
a13e2d5
pablogsal
pablogsal approved these changes Oct 5, 2026
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Comment thread Python/import.c Resolved

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Comment thread Misc/NEWS.d/next/Core_and_Builtins/2026-10-05-01-59-22.gh-issue-158820.3KLyOT.rst Resolved

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Comment thread Python/import.c Resolved

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting review labels Oct 5, 2026
@brittanyrey
Test _imp._set_lazy_attributes() at shutdown, add a comment and rewor…
b1651ea 
…d NEWS
@brittanyrey

brittanyrey commented Oct 5, 2026

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@brettcannon
brettcannon removed their request for review October 5, 2026 21:18
@encukou
encukou merged commit a6e6361 into python:main Oct 9, 2026
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@bedevere-app bedevere-app Bot removed the awaiting merge label Oct 9, 2026
@encukou encukou added awaiting merge needs backport to 3.15 bugs and security fixes labels Oct 9, 2026
@miss-islington-app

miss-islington-app Bot commented Oct 9, 2026

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Thanks @brittanyrey for the PR, and @encukou for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖
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@bedevere-app

bedevere-app Bot commented Oct 9, 2026

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GH-159062 is a backport of this pull request to the 3.15 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Oct 9, 2026
@brittanyrey
brittanyrey deleted the b-lazy-fini-null-state branch October 9, 2026 13:38
JelleZijlstra pushed a commit that referenced this pull request Oct 9, 2026
@miss-islington @brittanyrey
[3.15] gh-158820: Add null checks to avoid segfaults with lazy import…
f8375c2 
…s at shutdown (GH-158821) (#159062)

gh-158820: Add null checks to avoid segfaults with lazy imports at shutdown (GH-158821)

Destructors can run after finalization has cleared the interpreter's
lazy_modules set and lazy_pending_submodules dict. Declaring or
resolving a lazy import from one of them passed NULL to PySet_Add(),
PySet_Discard() or the pending-submodules lookup.

Treat the bookkeeping as a no-op once the state is gone, as the other
readers of this state already do.
(cherry picked from commit a6e6361)

Co-authored-by: Brittany Reynoso <[email protected]>
@pablogsal pablogsal mentioned this pull request Oct 9, 2026
Request for Python triage membership: Brittany Reynoso python/core-workflow#609
Closed
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@StanFromIreland StanFromIreland StanFromIreland left review comments
@pablogsal pablogsal pablogsal approved these changes
@Yhg1s Yhg1s Awaiting requested review from Yhg1s Yhg1s is a code owner
@DinoV DinoV Awaiting requested review from DinoV DinoV is a code owner
@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently is a code owner
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@FFY00 FFY00 Awaiting requested review from FFY00 FFY00 is a code owner
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4 participants

@brittanyrey @pablogsal @StanFromIreland @encukou
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