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atexit.unregister() can remove wrong callback #142881

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atexit.unregister() can remove wrong callback#142881
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serhiy-storchaka
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3.13only security fixes3.14bugs and security fixes3.15bugs and security fixesextension-modulesC modules in the Modules dirtype-bugAn unexpected behavior, bug, or error

Description

@serhiy-storchaka
serhiy-storchaka
opened on Dec 17, 2025

Bug report

atexit.unregister() can call the user __eq__() when it searches the callback(s) to remove. If __eq__() returns true, the callback is removed by index. But __eq__() can call arbitrary code, it can release the GIL, and atexit.unregister() can be called in other thread. If it removes the callback at the current index or before current index, the current index will no point to the compared callable, and the following deletion will delete wrong callable.

This issue is similar to #112127, but causes different symptoms.

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Activity

  1. serhiy-storchaka
    self-assigned this
    on Dec 17, 2025
  2. serhiy-storchaka
    added
    type-bugAn unexpected behavior, bug, or error
    3.13only security fixes
    3.14bugs and security fixes
    3.15bugs and security fixes
    on Dec 17, 2025

  3. johnslavik commented on Dec 17, 2025

    @johnslavik
    johnslavik
    on Dec 17, 2025
    Member

    @ZeroIntensity extension-modules

  4. ZeroIntensity
    added
    extension-modulesC modules in the Modules dir
    on Dec 17, 2025
  5. serhiy-storchaka
    added a commit that references this issue on Dec 17, 2025

    pythongh-142881: Fix concurrent and reentrant call of atexit.unregist…

    d79b714
  6. serhiy-storchaka
    added a commit that references this issue on Jan 12, 2026

    gh-142881: Fix concurrent and reentrant call of atexit.unregister() (G…

    dbd10a6
  7. miss-islington
    added a commit that references this issue on Jan 12, 2026

    pythongh-142881: Fix concurrent and reentrant call of atexit.unregist…

    790966f
  8. serhiy-storchaka
    added a commit that references this issue on Jan 12, 2026

    [3.13] pythongh-142881: Fix concurrent and reentrant call of atexit.u…

    c19a9d6

  9. serhiy-storchaka commented on Jan 12, 2026

    @serhiy-storchaka
    serhiy-storchaka
    on Jan 12, 2026
    MemberAuthor

    3.13 required completely different solution than 3.14+.

  10. serhiy-storchaka
    added a commit that references this issue on Jan 12, 2026

    [3.14] gh-142881: Fix concurrent and reentrant call of atexit.unregis…

    73d4445
  11. serhiy-storchaka
    closed this as completedon Jan 12, 2026
  12. serhiy-storchaka
    added a commit that references this issue on Jan 12, 2026

    [3.13] gh-142881: Fix concurrent and reentrant call of atexit.unregis…

    1822f59
  13. reidenong
    added a commit that references this issue on Jan 12, 2026

    pythongh-142881: Fix concurrent and reentrant call of atexit.unregist…

    f9d171a
  14. thunder-coding
    added a commit that references this issue on Feb 15, 2026

    pythongh-142881: Fix concurrent and reentrant call of atexit.unregist…

    ff519e0
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3.13only security fixes3.14bugs and security fixes3.15bugs and security fixesextension-modulesC modules in the Modules dirtype-bugAn unexpected behavior, bug, or error

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