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GeezerVison is showing github.com — gh-155109: Run tests exhausting the C stack with a limited C stack by serhiy-storchaka · Pull Request #155120 · python/cpython

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@serhiy-storchaka

@serhiy-storchaka serhiy-storchaka commented Aug 3, 2026 •
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Add the @support.run_with_limited_c_stack(depth) decorator: it runs the test in a thread with an 8 MiB C stack, so that the outcome does not depend on RLIMIT_STACK. If the thread stack size cannot be limited, it falls back to the old behavior — run in the current thread and skip if the C stack is too large.

Use it in tests which recurse to a fixed depth. @support.skip_if_huge_c_stack() estimates the remaining stack in interpreter loop frames (~328 bytes), so it fails to skip tests which recurse with much smaller C frames (~100 bytes) — they fail with a 16 MiB stack. It is kept for tests with unbounded recursion and for test_call.test_super_deep(), which needs a deep stack.

Tested on Linux with 1, 8, 16, 32 and 512 MiB and unlimited stack limits, and on illumos and OpenBSD.

  • Issue: skip_if_huge_c_stack underestimates available C recursion depth #155109

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@serhiy-storchaka @claude
pythongh-155109: Run tests exhausting the C stack with a limited C stack
1dfac0f 
Add the @support.run_with_limited_c_stack() decorator which runs the test
in a thread with a small C stack, so that the outcome does not depend on
RLIMIT_STACK. Use it in tests which recurse to a fixed depth --
@support.skip_if_huge_c_stack() failed to skip them with a 16 MiB stack.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
@serhiy-storchaka
serhiy-storchaka requested review from AlexWaygood, Eclips4, JelleZijlstra, iritkatriel and tomasr8 as code owners August 3, 2026 13:44
@bedevere-app bedevere-app Bot added the awaiting core review label Aug 3, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Aug 3, 2026
skip_if_huge_c_stack underestimates available C recursion depth #155109
Closed
@serhiy-storchaka @claude
Use a 8 MiB C stack in run_with_limited_c_stack()
74b489a 
On platforms where the interpreter cannot query the thread stack size it
assumes Py_C_STACK_SIZE (4 MiB), so a smaller thread stack crashes instead
of raising RecursionError. Verified on illumos and OpenBSD: a 2 MiB stack
dumps core, 8 MiB raises RecursionError.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
@serhiy-storchaka

serhiy-storchaka commented Aug 3, 2026

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@kulikjak, could you please test if this helps?
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@serhiy-storchaka @claude
Add a NEWS entry
4856144 
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
@AlexWaygood
AlexWaygood removed their request for review August 3, 2026 20:52
@serhiy-storchaka serhiy-storchaka mentioned this pull request Aug 4, 2026
test_detach_materialized_dict_no_memory depends on the exact number of allocations #155146
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@serhiy-storchaka

serhiy-storchaka commented Aug 4, 2026

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The failure of the Windows / Build and test (x64, tail-call) job is gh-155146: test_detach_materialized_dict_no_memory fails if any other allocation happens before the one which detaches the instance dictionary, and adding functions to test.support is enough to shift the sequence. Fixed in #155150.
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@kulikjak

kulikjak commented Aug 4, 2026

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Thanks! I tested your change and the test suite is green again.
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@serhiy-storchaka
Merge branch 'main' of https://github.com/python/cpython into pythong…
024188e 
…h-155109-limited-c-stack
@serhiy-storchaka
serhiy-storchaka enabled auto-merge (squash) August 4, 2026 09:15
@serhiy-storchaka serhiy-storchaka added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Aug 4, 2026
@serhiy-storchaka
serhiy-storchaka merged commit ce5ae29 into python:main Aug 4, 2026
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@miss-islington-app

miss-islington-app Bot commented Aug 4, 2026

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Thanks @serhiy-storchaka for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15.
🐍🍒⛏🤖
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@bedevere-app bedevere-app Bot removed the awaiting core review label Aug 4, 2026
@miss-islington-app

miss-islington-app Bot commented Aug 4, 2026

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Sorry, @serhiy-storchaka, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker ce5ae29ef9b8ccb32683c922d135339311c36c9d 3.14
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@miss-islington-app miss-islington-app Bot assigned serhiy-storchaka Aug 4, 2026
@bedevere-app

bedevere-app Bot commented Aug 4, 2026

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GH-155164 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 Aug 4, 2026
@bedevere-app

bedevere-app Bot commented Aug 4, 2026

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GH-155165 is a backport of this pull request to the 3.14 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Aug 4, 2026
serhiy-storchaka added a commit that referenced this pull request Aug 4, 2026
@serhiy-storchaka @claude
[3.14] gh-155109: Run tests exhausting the C stack with a limited C s…
b669be3 
…tack (GH-155120) (GH-155165)

Add the @support.run_with_limited_c_stack() decorator which runs the test
in a thread with a 8 MiB C stack, so that the outcome does not depend on
RLIMIT_STACK. Use it in tests which recurse to a fixed depth --
@support.skip_if_huge_c_stack() failed to skip them with a 16 MiB stack.

(cherry picked from commit ce5ae29)

Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
deadlovelll pushed a commit to deadlovelll/cpython that referenced this pull request Aug 5, 2026
@serhiy-storchaka @claude @deadlovelll
[3.14] pythongh-155109: Run tests exhausting the C stack with a limit…
f161c35 
…ed C stack (pythonGH-155120) (pythonGH-155165)

Add the @support.run_with_limited_c_stack() decorator which runs the test
in a thread with a 8 MiB C stack, so that the outcome does not depend on
RLIMIT_STACK. Use it in tests which recurse to a fixed depth --
@support.skip_if_huge_c_stack() failed to skip them with a 16 MiB stack.

(cherry picked from commit ce5ae29)

Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
mbeijen pushed a commit to mbeijen/cpython that referenced this pull request Aug 14, 2026
@serhiy-storchaka @claude @mbeijen
pythongh-155109: Run tests exhausting the C stack with a limited C st…
50c8389 
…ack (pythonGH-155120)

Add the @support.run_with_limited_c_stack() decorator which runs the test
in a thread with a 8 MiB C stack, so that the outcome does not depend on
RLIMIT_STACK. Use it in tests which recurse to a fixed depth --
@support.skip_if_huge_c_stack() failed to skip them with a 16 MiB stack.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
@serhiy-storchaka
serhiy-storchaka deleted the gh-155109-limited-c-stack branch August 27, 2026 12:34
@doko42 doko42 mentioned this pull request Sep 28, 2026
[3.14 Regression] test_typing.GenericTests.test_parameters_deep_recursion fails on arm-linux-gnueabihf #158314
Open
serhiy-storchaka added a commit that referenced this pull request Oct 10, 2026
@miss-islington @serhiy-storchaka @claude
[3.15] gh-155109: Run tests exhausting the C stack with a limited C s…
1f660c7 
…tack (GH-155120) (GH-155164)

Add the @support.run_with_limited_c_stack() decorator which runs the test
in a thread with a 8 MiB C stack, so that the outcome does not depend on
RLIMIT_STACK. Use it in tests which recurse to a fixed depth --
@support.skip_if_huge_c_stack() failed to skip them with a 16 MiB stack.
(cherry picked from commit ce5ae29)

Co-authored-by: Serhiy Storchaka <[email protected]>
Co-authored-by: Claude Opus 5 (1M context) <[email protected]>
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@JelleZijlstra JelleZijlstra Awaiting requested review from JelleZijlstra JelleZijlstra is a code owner
@iritkatriel iritkatriel Awaiting requested review from iritkatriel iritkatriel is a code owner
@Eclips4 Eclips4 Awaiting requested review from Eclips4 Eclips4 is a code owner
@tomasr8 tomasr8 Awaiting requested review from tomasr8 tomasr8 is a code owner

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@serhiy-storchaka @kulikjak
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