Description

Fidget-Spinner

opened on Nov 17, 2025

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Bug report

Bug description:

We invalidate executors in the following code:

static int
force_instrument_lock_held(PyCodeObject *code, PyInterpreterState *interp)

AND

_PyMonitoring_SetEvents(int tool_id, _PyMonitoringEventSet events)

In the above functions, the world is stopped/the runtime lock is acquired. However, the JIT can invalidate executors. If the pending executors list becomes full, executors will be finalized. This in turn means arbitrary code can run which may try to acquire the runtime lock and cause a deadlock.

I discovered this while working on FT JIT.

CPython versions tested on:

3.15, 3.14, CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-141658: JIT: lazy executor flush while the world is stopped #142329

Activity

1. Fidget-Spinner

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Nov 17, 2025
2. Fidget-Spinner commented on Nov 17, 2025

   

   Fidget-Spinner

   on Nov 17, 2025

   MemberAuthor

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   @markshannon
3. Fidget-Spinner

   self-assigned this

   on Nov 17, 2025
4. StanFromIreland

   added

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

   topic-JIT

   on Nov 17, 2025
5. Fidget-Spinner commented on Dec 5, 2025

   

   Fidget-Spinner

   on Dec 5, 2025

   MemberAuthor

   More actions

   One possible solution is to temporarily allow the list to be longer and ignore the current limit. Ie delay reclamation of executors in add_to_pending_deletion_list
6. markshannon commented on Dec 9, 2025

   

   markshannon

   on Dec 9, 2025

   Member

   More actions

   The problem is not the executor invalidation functions are called in unsafe ways, but that they are unsafe. We should be able to call them at any time.
7. Fidget-Spinner

   closed this as completedon Jan 4, 2026

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