Memory leak in test_sys with subinterpreters creation (AddressSanitizer detection)

[ashm-dev]

Bug report

Bug description:

Bug Description:

I've discovered a memory leak when running test_sys with AddressSanitizer enabled. The leak occurs during subinterpreter creation and the allocated memory is never freed.

Environment:

• CPython versions affected: 3.14 and 3.15 (main branch)
• Operating System: Linux (Ubuntu-based)
• Build configuration:

CC=clang CXX=clang++ ./configure \
    --disable-optimizations \
    --with-valgrind \
    --with-pydebug \
    --enable-pystats \
    --with-address-sanitizer

Steps to Reproduce:

1. Build CPython with the configuration above (tested on both 3.14 and main branches)
2. Run: ./python -m test test_sys
3. Observe AddressSanitizer output at the end

Expected Behavior:
No memory leaks should be detected by AddressSanitizer.

Actual Behavior:
AddressSanitizer reports approximately 4.5 MB leaked across 20 allocations. All allocations trace back to _PyInterpreterState_New → alloc_interpreter → _PyMem_DebugRawCalloc.

The test itself passes successfully, but the leak persists:

== Tests result: SUCCESS ==
1 test OK.
=================================================================
ERROR: LeakSanitizer: detected memory leaks

Reproduction on Multiple Versions:

• 3.14 branch: 4.5 MB leaked (4517100 bytes in 20 allocations)
• 3.15 (main): 4.5 MB leaked (4516460 bytes in 20 allocations)

Additional Context:

The leak appears to be related to subinterpreter lifecycle management. The stack trace shows memory is allocated through:

• interp_create (Modules/_interpretersmodule.c)
• _PyXI_NewInterpreter (Python/crossinterp.c:3204)
• Py_NewInterpreterFromConfig (Python/pylifecycle.c)
• new_interpreter (Python/pylifecycle.c)
• _PyInterpreterState_New (Python/pystate.c)
• alloc_interpreter (Python/pystate.c)

This issue appears to be related to #110411, which remains open with the latest report from August 2025 stating "This is still a problem in 3.13.7 and 3.14.0rc2". Issue #113055 was closed as resolved in February 2025, but the leak still occurs on current 3.14 and main branches.

Complete AddressSanitizer Output (3.15 main branch)

➜  main git:(main) sudo ./build/main/python -m test test_sys
Using random seed: 1335876681
0:00:00 load avg: 25.72 Run 1 test sequentially in a single process
0:00:00 load avg: 25.72 [1/1] test_sys
0:00:20 load avg: 27.57 [1/1] test_sys passed

== Tests result: SUCCESS ==

1 test OK.

Total duration: 20.6 sec
Total tests: run=92 skipped=6
Total test files: run=1/1
Result: SUCCESS

=================================================================
==544756==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 4290637 byte(s) in 19 object(s) allocated from:
    #0 0x5c153a3eef9d in calloc (/home/shamil/oss/cpython/main/build/main/python+0x33bf9d) (BuildId: c97dc91acec24b8d7d7a9344676b1bb0726ae568)
    #1 0x5c153a777a5e in _PyMem_DebugRawAlloc /home/shamil/oss/cpython/main/build/main/../../Objects/obmalloc.c:2884:24
    #2 0x5c153a777a5e in _PyMem_DebugRawCalloc /home/shamil/oss/cpython/main/build/main/../../Objects/obmalloc.c:2929:12
    #3 0x5c153abd8578 in alloc_interpreter /home/shamil/oss/cpython/main/build/main/../../Python/pystate.c:462:17
    #4 0x5c153abd8578 in _PyInterpreterState_New /home/shamil/oss/cpython/main/build/main/../../Python/pystate.c:660:18
    #5 0x5c153ab8e818 in new_interpreter /home/shamil/oss/cpython/main/build/main/../../Python/pylifecycle.c:2425:14
    #6 0x5c153ab8e592 in Py_NewInterpreterFromConfig /home/shamil/oss/cpython/main/build/main/../../Python/pylifecycle.c:2521:12
    #7 0x5c153aab1b58 in _PyXI_NewInterpreter /home/shamil/oss/cpython/main/build/main/../../Python/crossinterp.c:3204:23
    #8 0x726f325c23ae in _interpreters_create_impl /home/shamil/oss/cpython/main/build/main/../../Modules/_interpretersmodule.c:880:13
    #9 0x726f325c23ae in _interpreters_create /home/shamil/oss/cpython/main/build/main/../../Modules/clinic/_interpretersmodule.c.h:91:20
    #10 0x5c153a5e91c2 in _PyObject_VectorcallTstate /home/shamil/oss/cpython/main/build/main/../../Include/internal/pycore_call.h:169:11
    #11 0x5c153aa11ff6 in _PyEval_EvalFrameDefault /home/shamil/oss/cpython/main/build/main/../../Python/generated_cases.c.h:3188:35
    [... rest of stack trace truncated for brevity ...]

Direct leak of 225823 byte(s) in 1 object(s) allocated from:
    #0 0x5c153a3eef9d in calloc (/home/shamil/oss/cpython/main/build/main/python+0x33bf9d) (BuildId: c97dc91acec24b8d7d7a9344676b1bb0726ae568)
    #1 0x5c153a777a5e in _PyMem_DebugRawAlloc /home/shamil/oss/cpython/main/build/main/../../Objects/obmalloc.c:2884:24
    #2 0x5c153a777a5e in _PyMem_DebugRawCalloc /home/shamil/oss/cpython/main/build/main/../../Objects/obmalloc.c:2929:12
    #3 0x5c153abd8578 in alloc_interpreter /home/shamil/oss/cpython/main/build/main/../../Python/pystate.c:462:17
    #4 0x5c153abd8578 in _PyInterpreterState_New /home/shamil/oss/cpython/main/build/main/../../Python/pystate.c:660:18
    [... rest of stack trace truncated for brevity ...]

SUMMARY: AddressSanitizer: 4516460 byte(s) leaked in 20 allocation(s).

Complete AddressSanitizer Output (3.14 branch)

➜  3.14 git:(3.14) sudo ./python -m test test_sys
Using random seed: 641571276
0:00:00 load avg: 2.97 Run 1 test sequentially in a single process
0:00:00 load avg: 2.97 [1/1] test_sys
0:00:06 load avg: 2.66 [1/1] test_sys passed

== Tests result: SUCCESS ==

1 test OK.

Total duration: 6.7 sec
Total tests: run=97 skipped=7
Total test files: run=1/1
Result: SUCCESS

=================================================================
==570353==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 4291245 byte(s) in 19 object(s) allocated from:
    #0 0x5ea8303c6f8d in calloc (/home/shamil/oss/cpython/3.14/python+0x325f8d) (BuildId: bd4e3657446f867dffe5f140bfa56307be2c714a)
    #1 0x5ea83074b5be in _PyMem_DebugRawAlloc /home/shamil/oss/cpython/3.14/Objects/obmalloc.c:2869:24
    #2 0x5ea83074b5be in _PyMem_DebugRawCalloc /home/shamil/oss/cpython/3.14/Objects/obmalloc.c:2914:12
    #3 0x5ea830b8f5ec in alloc_interpreter /home/shamil/oss/cpython/3.14/Python/pystate.c:570:17
    #4 0x5ea830b8f5ec in _PyInterpreterState_New /home/shamil/oss/cpython/3.14/Python/pystate.c:757:18
    #5 0x5ea830b5a2c8 in new_interpreter /home/shamil/oss/cpython/3.14/Python/pylifecycle.c:2313:14
    #6 0x5ea830b5a042 in Py_NewInterpreterFromConfig /home/shamil/oss/cpython/3.14/Python/pylifecycle.c:2409:12
    #7 0x5ea830a7cd78 in _PyXI_NewInterpreter /home/shamil/oss/cpython/3.14/Python/crossinterp.c:3204:23
    #8 0x7be02a35a2a8 in interp_create /home/shamil/oss/cpython/3.14/./Modules/_interpretersmodule.c:862:13
    [... rest of stack trace truncated for brevity ...]

Direct leak of 225855 byte(s) in 1 object(s) allocated from:
    #0 0x5ea8303c6f8d in calloc (/home/shamil/oss/cpython/3.14/python+0x325f8d) (BuildId: bd4e3657446f867dffe5f140bfa56307be2c714a)
    #1 0x5ea83074b5be in _PyMem_DebugRawAlloc /home/shamil/oss/cpython/3.14/Objects/obmalloc.c:2869:24
    #2 0x5ea83074b5be in _PyMem_DebugRawCalloc /home/shamil/oss/cpython/3.14/Objects/obmalloc.c:2914:12
    #3 0x5ea830b8f5ec in alloc_interpreter /home/shamil/oss/cpython/3.14/Python/pystate.c:570:17
    #4 0x5ea830b8f5ec in _PyInterpreterState_New /home/shamil/oss/cpython/3.14/Python/pystate.c:757:18
    [... rest of stack trace truncated for brevity ...]

SUMMARY: AddressSanitizer: 4517100 byte(s) leaked in 20 allocation(s).

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

[picnixz]

@ericsnowcurrently It appears we still have a leak in subinterpreters. It also looks like similar to #110411 but not really a duplicate considering the traceback.

[ashm-dev]

I'll try to fix this leak, but no promises.

[picnixz]

Let us first try to check if this is something that is known to Eric or not before jumping onto a PR. It would avoid having to make unnecessary work. It's fine to report an issue, wait for an expert to have a look at it, and only then consider a PR.

[ashm-dev]

Alright, got it, I’ll do that. Thanks!