TSan: data race with PyTypeObject version tag

[pitrou]

Bug report

Bug description:

Running test_capi with TSan enabled and the GIL enabled yields the following race condition:

test_isolated_subinterpreter (test.test_capi.test_misc.TestPendingCalls.test_isolated_subinterpreter) ... 
==================
WARNING: ThreadSanitizer: data race (pid=84714)
  Read of size 4 at 0x55c8c4c10f90 by thread T1:
    #0 assign_version_tag /home/antoine/cpython/default/Objects/typeobject.c:1012:13 (python+0x327919) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #1 _PyType_Lookup /home/antoine/cpython/default/Objects/typeobject.c:5087:23 (python+0x3290ab) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #2 _PyObject_GetMethod /home/antoine/cpython/default/Objects/object.c:1462:23 (python+0x2d9f67) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #3 _PyEval_EvalFrameDefault /home/antoine/cpython/default/Python/generated_cases.c.h:3561:25 (python+0x443799) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #4 _PyEval_EvalFrame /home/antoine/cpython/default/./Include/internal/pycore_ceval.h:114:16 (python+0x26cd12) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #5 gen_send_ex2 /home/antoine/cpython/default/Objects/genobject.c:228:24 (python+0x26cd12)
    #6 gen_iternext /home/antoine/cpython/default/Objects/genobject.c:586:9 (python+0x26a0d2) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #7 builtin_next /home/antoine/cpython/default/Python/bltinmodule.c:1534:11 (python+0x4172a3) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
[...]

  Previous write of size 4 at 0x55c8c4c10f90 by main thread:
    #0 assign_version_tag /home/antoine/cpython/default/Objects/typeobject.c (python+0x32794d) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #1 _PyType_Lookup /home/antoine/cpython/default/Objects/typeobject.c:5087:23 (python+0x3290ab) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #2 _PyObject_GetMethod /home/antoine/cpython/default/Objects/object.c:1462:23 (python+0x2d9f67) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #3 _PyEval_EvalFrameDefault /home/antoine/cpython/default/Python/generated_cases.c.h:3561:25 (python+0x443799) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #4 _PyEval_EvalFrame /home/antoine/cpython/default/./Include/internal/pycore_ceval.h:114:16 (python+0x26cd12) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #5 gen_send_ex2 /home/antoine/cpython/default/Objects/genobject.c:228:24 (python+0x26cd12)
    #6 gen_iternext /home/antoine/cpython/default/Objects/genobject.c:586:9 (python+0x26a0d2) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)
    #7 builtin_next /home/antoine/cpython/default/Python/bltinmodule.c:1534:11 (python+0x4172a3) (BuildId: 80a378e5bf8e9a3b503d1ddb455283576a308db6)

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-116909: fix data race with versions in typeobject #134651

[pitrou]

@colesbury @ericsnowcurrently

[pitrou]

From what I can see, the problem is accessing _PyRuntime.types.next_version_tag without synchronization and without atomic instructions.