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Python 3.14.0a5 i686 Linux freethreading-debug build fails: gc_free_threading.c:1077: mark_heap_visitor: Assertion "gc_get_refs(op) >= 0" failed: refcount is too small #130030

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befeleme opened this issue Feb 12, 2025 · 2 comments
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Python 3.14.0a5 i686 Linux freethreading-debug build fails: gc_free_threading.c:1077: mark_heap_visitor: Assertion "gc_get_refs(op) >= 0" failed: refcount is too small #130030

befeleme opened this issue Feb 12, 2025 · 2 comments
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3.14 bugs and security fixes build The build process and cross-build topic-free-threading type-bug An unexpected behavior, bug, or error

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@befeleme
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befeleme commented Feb 12, 2025 •
edited by bedevere-app bot
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Bug report

Bug description:

I try to build freethreading-debug Python 3.14.0a5 for i686 Fedora Linux with a consistent failure: /builddir/build/BUILD/python3.14-3.14.0_a5-build/Python-3.14.0a5/Python/gc_free_threading.c:1077: mark_heap_visitor: Assertion "gc_get_refs(op) >= 0" failed: refcount is too small. This happens when freezing importlib._bootstrap_external, zipimport, importlib._bootstrap.
The bigger log excerpt:

./Programs/_freeze_module getpath /builddir/build/BUILD/python3.14-3.14.0_a5-build/Python-3.14.0a5/Modules/getpath.py Python/frozen_modules/getpath.h
./Programs/_freeze_module importlib._bootstrap_external /builddir/build/BUILD/python3.14-3.14.0_a5-build/Python-3.14.0a5/Lib/importlib/_bootstrap_external.py Python/frozen_modules/importlib._bootstrap_external.h
/builddir/build/BUILD/python3.14-3.14.0_a5-build/Python-3.14.0a5/Python/gc_free_threading.c:1077: mark_heap_visitor: Assertion "gc_get_refs(op) >= 0" failed: refcount is too small
Enable tracemalloc to get the memory block allocation traceback
object address  : 0xefc48188
object refcount : 1
object type     : 0x56bef880
object type name: staticmethod
object repr     : <staticmethod(<built-in method maketrans of type object at 0x56be6ac0>)>
Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed
Python runtime state: core initialized
Stack (most recent call first):
  <no Python frame>
make: *** [Makefile:1772: Python/frozen_modules/importlib._bootstrap_external.h] Aborted (core dumped)
make: *** Waiting for unfinished jobs....
./Programs/_freeze_module zipimport /builddir/build/BUILD/python3.14-3.14.0_a5-build/Python-3.14.0a5/Lib/zipimport.py Python/frozen_modules/zipimport.h
/builddir/build/BUILD/python3.14-3.14.0_a5-build/Python-3.14.0a5/Python/gc_free_threading.c:1077: mark_heap_visitor: Assertion "gc_get_refs(op) >= 0" failed: refcount is too small
Enable tracemalloc to get the memory block allocation traceback
object address  : 0xefc48188
object refcount : 1
object type     : 0x56be0880
object type name: staticmethod
object repr     : <staticmethod(<built-in method maketrans of type object at 0x56bd7ac0>)>
Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed
Python runtime state: core initialized
Stack (most recent call first):
  <no Python frame>
make: *** [Makefile:1775: Python/frozen_modules/zipimport.h] Aborted (core dumped)
./Programs/_freeze_module importlib._bootstrap /builddir/build/BUILD/python3.14-3.14.0_a5-build/Python-3.14.0a5/Lib/importlib/_bootstrap.py Python/frozen_modules/importlib._bootstrap.h
/builddir/build/BUILD/python3.14-3.14.0_a5-build/Python-3.14.0a5/Python/gc_free_threading.c:1077: mark_heap_visitor: Assertion "gc_get_refs(op) >= 0" failed: refcount is too small
Enable tracemalloc to get the memory block allocation traceback
object address  : 0xefc48188
object refcount : 1
object type     : 0x56bb7880
object type name: staticmethod
object repr     : <staticmethod(<built-in method maketrans of type object at 0x56baeac0>)>
Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed
Python runtime state: core initialized
Stack (most recent call first):
  <no Python frame>
make: *** [Makefile:1769: Python/frozen_modules/importlib._bootstrap.h] Aborted (core dumped)

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs
@befeleme befeleme added the type-bug An unexpected behavior, bug, or error label Feb 12, 2025
@hugovk hugovk added topic-free-threading 3.14 bugs and security fixes labels Feb 12, 2025
@picnixz picnixz added the build The build process and cross-build label Feb 12, 2025
@colesbury
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Thanks, I'm able to repro this and should have a fix soon.

colesbury added a commit to colesbury/cpython that referenced this issue Feb 12, 2025
@colesbury
pythongh-130030: Fix crash on 32-bit Linux with free threading
a3648df 
The `gc_get_refs` assertion needs to be after we check the alive and
unreachable bits. Otherwise, `ob_tid` may store the actual thread id
instead of the computed `gc_refs`, which may trigger the assertion if
the `ob_tid` looks like a negative value.

Also fix a few type warnings on 32-bit systems.
@bedevere-app bedevere-app bot mentioned this issue Feb 12, 2025
Merged
colesbury added a commit that referenced this issue Feb 12, 2025
@colesbury
gh-130030: Fix crash on 32-bit Linux with free threading (gh-130043)
e094420 
The `gc_get_refs` assertion needs to be after we check the alive and
unreachable bits. Otherwise, `ob_tid` may store the actual thread id
instead of the computed `gc_refs`, which may trigger the assertion if
the `ob_tid` looks like a negative value.

Also fix a few type warnings on 32-bit systems.
@befeleme
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Thank you, the fix indeed solves the issue in my build.

befeleme pushed a commit to fedora-python/cpython that referenced this issue Mar 17, 2025
@colesbury @befeleme
00451: pythongh-130030: Fix crash on 32-bit Linux with free threading (…
cce21a6 
…pythongh-130043)

The `gc_get_refs` assertion needs to be after we check the alive and
unreachable bits. Otherwise, `ob_tid` may store the actual thread id
instead of the computed `gc_refs`, which may trigger the assertion if
the `ob_tid` looks like a negative value.

Also fix a few type warnings on 32-bit systems.
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