BUG: Race in computing initial value for reductions under free-threading #28041
Description
Describe the issue:
With:
- CPython 3.13 built with the GIL disabled, using thread-sanitizer under clang,
- NumPy 2.3.0dev commit 35b2c4a built with thread-sanitizer and clang
thread sanitizer reports a race constructing the cached initial value for a reducer.
You may need to run the example a few times, but it reproduced first time for me.
Reproduce the code example:
import concurrent.futures
import threading
import numpy as np
num_threads = 8
x = np.arange(1000)
b = threading.Barrier(num_threads)
def closure():
b.wait()
np.sum(x)
with concurrent.futures.ThreadPoolExecutor(max_workers=num_threads) as executor:
for _ in range(num_threads):
executor.submit(closure)Error message:
WARNING: ThreadSanitizer: data race (pid=4069590)
Write of size 8 at 0x7f6412728ef8 by thread T135:
#0 get_initial_from_ufunc legacy_array_method.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3de246) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#1 PyUFunc_ReduceWrapper <null> (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3e0426) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#2 PyUFunc_Reduce ufunc_object.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3f0349) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#3 PyUFunc_GenericReduction ufunc_object.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3efffa) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#4 ufunc_reduce ufunc_object.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3ed841) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#5 cfunction_vectorcall_FASTCALL_KEYWORDS /usr/local/google/home/phawkins/p/cpython/Objects/methodobject.c:441:24 (python3.13+0x28a010) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#6 _PyVectorcall_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:273:16 (python3.13+0x1eb293) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#7 _PyObject_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:348:16 (python3.13+0x1eb293)
#8 PyObject_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:373:12 (python3.13+0x1eb315) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#9 _PyEval_EvalFrameDefault /usr/local/google/home/phawkins/p/cpython/Python/generated_cases.c.h:1355:26 (python3.13+0x3e46e2) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#10 _PyEval_EvalFrame /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_ceval.h:119:16 (python3.13+0x3de62a) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#11 _PyEval_Vector /usr/local/google/home/phawkins/p/cpython/Python/ceval.c:1811:12 (python3.13+0x3de62a)
#12 _PyFunction_Vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/call.c (python3.13+0x1eb61f) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#13 _PyObject_VectorcallTstate /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_call.h:168:11 (python3.13+0x1eafaa) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#14 PyObject_Vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/call.c:327:12 (python3.13+0x1eafaa)
#15 dispatcher_vectorcall arrayfunction_override.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x22d22b) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#16 _PyObject_VectorcallTstate /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_call.h:168:11 (python3.13+0x1eafaa) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#17 PyObject_Vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/call.c:327:12 (python3.13+0x1eafaa)
#18 _PyEval_EvalFrameDefault /usr/local/google/home/phawkins/p/cpython/Python/generated_cases.c.h:813:23 (python3.13+0x3e24fb) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#19 _PyEval_EvalFrame /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_ceval.h:119:16 (python3.13+0x3de62a) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#20 _PyEval_Vector /usr/local/google/home/phawkins/p/cpython/Python/ceval.c:1811:12 (python3.13+0x3de62a)
#21 _PyFunction_Vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/call.c (python3.13+0x1eb61f) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#22 _PyObject_VectorcallTstate /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_call.h:168:11 (python3.13+0x1ef5ef) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#23 method_vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/classobject.c:70:20 (python3.13+0x1ef5ef)
#24 _PyVectorcall_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:273:16 (python3.13+0x1eb293) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#25 _PyObject_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:348:16 (python3.13+0x1eb293)
#26 PyObject_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:373:12 (python3.13+0x1eb315) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#27 thread_run /usr/local/google/home/phawkins/p/cpython/./Modules/_threadmodule.c:337:21 (python3.13+0x564292) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#28 pythread_wrapper /usr/local/google/home/phawkins/p/cpython/Python/thread_pthread.h:243:5 (python3.13+0x4bd637) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
Previous write of size 8 at 0x7f6412728ef8 by thread T131:
#0 get_initial_from_ufunc legacy_array_method.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3de246) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#1 PyUFunc_ReduceWrapper <null> (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3e0426) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#2 PyUFunc_Reduce ufunc_object.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3f0349) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#3 PyUFunc_GenericReduction ufunc_object.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3efffa) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#4 ufunc_reduce ufunc_object.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x3ed841) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#5 cfunction_vectorcall_FASTCALL_KEYWORDS /usr/local/google/home/phawkins/p/cpython/Objects/methodobject.c:441:24 (python3.13+0x28a010) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#6 _PyVectorcall_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:273:16 (python3.13+0x1eb293) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#7 _PyObject_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:348:16 (python3.13+0x1eb293)
#8 PyObject_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:373:12 (python3.13+0x1eb315) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#9 _PyEval_EvalFrameDefault /usr/local/google/home/phawkins/p/cpython/Python/generated_cases.c.h:1355:26 (python3.13+0x3e46e2) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#10 _PyEval_EvalFrame /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_ceval.h:119:16 (python3.13+0x3de62a) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#11 _PyEval_Vector /usr/local/google/home/phawkins/p/cpython/Python/ceval.c:1811:12 (python3.13+0x3de62a)
#12 _PyFunction_Vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/call.c (python3.13+0x1eb61f) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#13 _PyObject_VectorcallTstate /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_call.h:168:11 (python3.13+0x1eafaa) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#14 PyObject_Vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/call.c:327:12 (python3.13+0x1eafaa)
#15 dispatcher_vectorcall arrayfunction_override.c (_multiarray_umath.cpython-313t-x86_64-linux-gnu.so+0x22d22b) (BuildId: a138a702a237ca030803af4168ee423ada9702f7)
#16 _PyObject_VectorcallTstate /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_call.h:168:11 (python3.13+0x1eafaa) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#17 PyObject_Vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/call.c:327:12 (python3.13+0x1eafaa)
#18 _PyEval_EvalFrameDefault /usr/local/google/home/phawkins/p/cpython/Python/generated_cases.c.h:813:23 (python3.13+0x3e24fb) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#19 _PyEval_EvalFrame /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_ceval.h:119:16 (python3.13+0x3de62a) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#20 _PyEval_Vector /usr/local/google/home/phawkins/p/cpython/Python/ceval.c:1811:12 (python3.13+0x3de62a)
#21 _PyFunction_Vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/call.c (python3.13+0x1eb61f) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#22 _PyObject_VectorcallTstate /usr/local/google/home/phawkins/p/cpython/./Include/internal/pycore_call.h:168:11 (python3.13+0x1ef5ef) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#23 method_vectorcall /usr/local/google/home/phawkins/p/cpython/Objects/classobject.c:70:20 (python3.13+0x1ef5ef)
#24 _PyVectorcall_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:273:16 (python3.13+0x1eb293) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#25 _PyObject_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:348:16 (python3.13+0x1eb293)
#26 PyObject_Call /usr/local/google/home/phawkins/p/cpython/Objects/call.c:373:12 (python3.13+0x1eb315) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#27 thread_run /usr/local/google/home/phawkins/p/cpython/./Modules/_threadmodule.c:337:21 (python3.13+0x564292) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)
#28 pythread_wrapper /usr/local/google/home/phawkins/p/cpython/Python/thread_pthread.h:243:5 (python3.13+0x4bd637) (BuildId: 9c1c16fb1bb8a435fa6fa4c6944da5d41f654e96)Python and NumPy Versions:
2.3.0.dev0+git20241219.35b2c4a
3.13.1 experimental free-threading build (tags/v3.13.1:06714517797, Dec 15 2024, 15:38:01) [Clang 18.1.8 (11)]
Runtime Environment:
[{'numpy_version': '2.3.0.dev0+git20241219.35b2c4a',
'python': '3.13.1 experimental free-threading build '
'(tags/v3.13.1:06714517797, Dec 15 2024, 15:38:01) [Clang 18.1.8 '
'(11)]',
'uname': uname_result(system='Linux', node='', release='', version='#1 SMP PREEMPT_DYNAMIC Debian 6.redacted (2024-10-16)', machine='x86_64')},
{'simd_extensions': {'baseline': ['SSE', 'SSE2', 'SSE3'],
'found': ['SSSE3',
'SSE41',
'POPCNT',
'SSE42',
'AVX',
'F16C',
'FMA3',
'AVX2'],
'not_found': ['AVX512F',
'AVX512CD',
'AVX512_KNL',
'AVX512_SKX',
'AVX512_CLX',
'AVX512_CNL',
'AVX512_ICL']}},
{'architecture': 'Zen',
'filepath': '/usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.27.so',
'internal_api': 'openblas',
'num_threads': 128,
'prefix': 'libopenblas',
'threading_layer': 'pthreads',
'user_api': 'blas',
'version': '0.3.27'}]
Context for the issue:
Found when working on free-threading support in JAX.