Description

nascheme

opened on Sep 27, 2024

Issue body actions

We occasionally fix these kinds of bugs, like GH-102356. However, the fix by adding the "trashcan" macros to the tp_dealloc method only fixes that specific type. It would be better to have a more generic fix. A crash due to the C stack overflow leaves the user mystified as to what the problem is and these kinds of bugs could be hard to reproduce (requiring long chains of objects calling tp_dealloc recursively).

Linked PRs

• GH-124715: trashcan protection for all GC objects #124716
• GH-124715: Move trashcan mechanism into Py_Dealloc #132280
• gh-124715: Fix method_dealloc(): use PyObject_GC_UnTrack() #133199
• Revert "gh-124715: Fix method_dealloc(): use PyObject_GC_UnTrack() (#133199)" #133434

Activity

1. nascheme

   added

   type-crashA hard crash of the interpreter, possibly with a core dumpA hard crash of the interpreter, possibly with a core dump

   on Sep 27, 2024
2. markshannon

   added a commit that references this issue on Apr 30, 2025

   GH-124715: Move trashcan mechanism into `Py_Dealloc` (GH-132280)

   44e4c47
3. vstinner

   added a commit that references this issue on May 1, 2025

   gh-124715: Fix method_dealloc(): use PyObject_GC_UnTrack() (#133199)

   662dd29
4. nascheme commented on May 1, 2025

   

   nascheme

   on May 1, 2025

   MemberAuthor

   More actions

   Regarding untracking, when I was working on my "integrate trashcan PR", I started wondering if _PyObject_GC_UNTRACK() should just be changed to check if the object is already untracked and not crash. I originally made it not safe to call twice because I wanted the tiny performance benefit (avoid the branch, I wanted GC support to have as little extra overhead as possible). However, in retrospect, I think it was a mistake. Knowing when it is safe to call _PyObject_GC_UNTRACK() in theory is possible but in practice it gets really painful. If you look at typeobject.c, it has to take great care to avoid _PyObject_GC_UNTRACK() from crashing.

   Maybe we should profile this and see if it has any performance impact at all? There has been many bugs related to this over the years.
5. vstinner

   added 2 commits that reference this issue on May 5, 2025

   Revert "pythongh-124715: Fix method_dealloc(): use PyObject_GC_UnTrac…

   7ce29b0

   Revert "gh-124715: Fix method_dealloc(): use PyObject_GC_UnTrack() (#…

   c336f1c
6. picnixz

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on May 17, 2025
7. Pranjal095

   added a commit that references this issue on Jul 12, 2025

   Revert "pythongh-124715: Fix method_dealloc(): use PyObject_GC_UnTrac…

   ad5f435
8. nascheme commented on Jul 14, 2025

   

   nascheme

   on Jul 14, 2025

   MemberAuthor

   More actions

   I believe this issue has been fixed with GH-132280.

   Reacted by Victor Stinner
9. nascheme

   closed this as completedon Jul 14, 2025
10. mandolaerik

    added a commit that references this issue on Jan 23, 2026

    Revert "pythonGH-124715: Move trashcan mechanism into `Py_Dealloc` (p…

    236e1bd

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