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gh-146527: Fix memory leak in _PyGC_Fini()#150969

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python:mainfrom
vstinner:free_gc
Jun 5, 2026
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gh-146527: Fix memory leak in _PyGC_Fini()#150969
vstinner merged 2 commits into
python:mainfrom
vstinner:free_gc

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@vstinner

@vstinner vstinner commented Jun 5, 2026 •
edited by bedevere-app Bot
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Free generation_stats allocated by _PyGC_Init().

Fix Python/gc.c: Python/gc_free_threading.c was already fixed.

@vstinner
pythongh-146527: Fix memory leak in _PyGC_Fini()
18b231f 
Free generation_stats allocated by _PyGC_Init().

Fix Python/gc.c: Python/gc_free_threading.c was already fixed.
@vstinner vstinner added the needs backport to 3.15 pre-release feature fixes, bugs and security fixes label Jun 5, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Jun 5, 2026
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@vstinner

vstinner commented Jun 5, 2026

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For example, the leak can be seen with Valgrind.

$ PYTHONMALLOC=malloc valgrind --leak-check=full --show-leak-kinds=all --num-callers=20 ./python -c pass
(...)
==3201846== HEAP SUMMARY:
==3201846==     in use at exit: 1,112 bytes in 1 blocks
==3201846==   total heap usage: 28,765 allocs, 28,764 frees, 6,620,982 bytes allocated
==3201846== 
==3201846== 1,112 bytes in 1 blocks are still reachable in loss record 1 of 1
==3201846==    at 0x484862B: calloc (vg_replace_malloc.c:1616)
==3201846==    by 0x4FE115: _PyMem_RawCalloc (obmalloc.c:80)
==3201846==    by 0x511FC1: PyMem_RawCalloc (obmalloc.c:1222)
==3201846==    by 0x62A744: _PyGC_Init (gc.c:137)
==3201846==    by 0x65DB65: pycore_interp_init (pylifecycle.c:975)
==3201846==    by 0x65DD71: pyinit_config (pylifecycle.c:1040)
==3201846==    by 0x666D3A: pyinit_core (pylifecycle.c:1203)
==3201846==    by 0x666E13: Py_InitializeFromConfig (pylifecycle.c:1631)
==3201846==    by 0x69888E: pymain_init (main.c:69)
==3201846==    by 0x698953: pymain_main (main.c:817)
==3201846==    by 0x6989E4: Py_BytesMain (main.c:850)
==3201846==    by 0x401CEE: main (python.c:15)
==3201846== 
==3201846== LEAK SUMMARY:
==3201846==    definitely lost: 0 bytes in 0 blocks
==3201846==    indirectly lost: 0 bytes in 0 blocks
==3201846==      possibly lost: 0 bytes in 0 blocks
==3201846==    still reachable: 1,112 bytes in 1 blocks
==3201846==         suppressed: 0 bytes in 0 blocks
(...)

I found the leak when building Python with ASAN.

@vstinner vstinner mentioned this pull request Jun 5, 2026
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@vstinner vstinner enabled auto-merge (squash) June 5, 2026 13:13
@pablogsal

pablogsal commented Jun 5, 2026

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Thanks victor!

@vstinner vstinner merged commit 0036565 into python:main Jun 5, 2026
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@vstinner vstinner deleted the free_gc branch June 5, 2026 13:43
@miss-islington-app

miss-islington-app Bot commented Jun 5, 2026

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Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

@bedevere-app

bedevere-app Bot commented Jun 5, 2026

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GH-150970 is a backport of this pull request to the 3.15 branch.

@bedevere-app bedevere-app Bot removed the needs backport to 3.15 pre-release feature fixes, bugs and security fixes label Jun 5, 2026
vstinner added a commit that referenced this pull request Jun 5, 2026
@miss-islington @vstinner
[3.15] gh-146527: Fix memory leak in _PyGC_Fini() (GH-150969) (#150970)
06ffcde 
gh-146527: Fix memory leak in _PyGC_Fini() (GH-150969)

Free generation_stats allocated by _PyGC_Init().

Fix Python/gc.c: Python/gc_free_threading.c was already fixed.
(cherry picked from commit 0036565)

Co-authored-by: Victor Stinner <vstinner@python.org>
@sergey-miryanov

sergey-miryanov commented Jun 5, 2026

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Thanks!

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