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GeezerVison is showing github.com — gh-157519: Don't defer deallocation on an unknown stack by JamesWrigley · Pull Request #157520 · python/cpython

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@JamesWrigley

@JamesWrigley JamesWrigley commented Sep 14, 2026 •
edited by bedevere-app Bot
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_Py_RecursionLimit_GetMargin() now reports plenty of margin when the stack pointer is far outside the stack limits, the same rule _Py_CheckRecursiveCall() uses to detect stack switching. Previously _Py_Dealloc() deferred every GC object to the trash queue on such a stack and the objects were never freed.

Fixes #157519. Output of the MWE on my machine:

real stack limits            __del__ calls:  1000/1000   traced memory:     0.0 MiB
stack limits far away        __del__ calls:  1000/1000   traced memory:     0.0 MiB
limits restored              __del__ calls:  1000/1000   traced memory:     0.0 MiB

Written with help from Claude 🤖 Though I reviewed and tested all the changes myself. I think this should be backported to 3.14?

  • Issue: _Py_Dealloc() being unaware of separate stacks can cause memory leaks #157519

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@JamesWrigley
pythongh-157519: Don't defer deallocation on an unknown stack
dee85ff 
`_Py_RecursionLimit_GetMargin()` now reports plenty of margin when the stack
pointer is far outside the stack limits, the same rule
`_Py_CheckRecursiveCall()` uses to detect stack switching. Previously
`_Py_Dealloc()` deferred every GC object to the trash queue on such a stack and
the chain was never destroyed.
@JamesWrigley
JamesWrigley requested review from FFY00, ZeroIntensity and ericsnowcurrently as code owners September 14, 2026 19:36
@python-cla-bot

python-cla-bot Bot commented Sep 14, 2026 •
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All commit authors signed the Contributor License Agreement.

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@bedevere-app bedevere-app Bot mentioned this pull request Sep 14, 2026
_Py_Dealloc() being unaware of separate stacks can cause memory leaks #157519
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@bedevere-app bedevere-app Bot added the awaiting review label Sep 14, 2026
@JamesWrigley

JamesWrigley commented Sep 16, 2026

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(AFAICT the test timeout is unrelated)
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@JamesWrigley JamesWrigley mentioned this pull request Oct 12, 2026
Python 3.14 stack overflow detection is incompatible with C++ Boost make_fcontext() coroutines #139653
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@vstinner

vstinner commented Oct 12, 2026

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cc @markshannon @encukou
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@encukou

encukou commented Oct 16, 2026

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@markshannon, does this fit the design?
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@JamesWrigley

JamesWrigley commented Oct 30, 2026

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(gentle bump)
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@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently is a code owner
@ZeroIntensity ZeroIntensity Awaiting requested review from ZeroIntensity ZeroIntensity is a code owner
@FFY00 FFY00 Awaiting requested review from FFY00 FFY00 is a code owner

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@JamesWrigley @vstinner @encukou
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