TSAN alarm in dictobject.c while using setattr #144774
Description
Bug report
Bug description:
While working around with my previous issue, I found another TSAN alarm.
from threading import Thread
import random
import copy
E = Exception()
def test1():
for _ in range(100):
setattr(E, 'x', random.randint(0,1000))
copy.copy(E)
def main():
threads = []
for _ in range(4):
threads.append(Thread(target=test1))
for t in threads:
t.start()
for t in threads:
t.join()
if __name__ == "__main__":
main()TSAN report:
WARNING: ThreadSanitizer: data race (pid=455134)
Read of size 8 at 0x7fffb60c01b0 by thread T1:
#0 _PyDict_Next /cpython/Objects/dictobject.c:3020:40 (python3.15t+0x291d09)
#1 PyDict_Next /cpython/Objects/dictobject.c:3074:12 (python3.15t+0x291d09)
#2 BaseException___setstate___impl /cpython/Objects/exceptions.c:245:16 (python3.15t+0x232246)
#3 BaseException___setstate__ /cpython/Objects/clinic/exceptions.c.h:48:20 (python3.15t+0x232246)
#4 method_vectorcall_O /cpython/Objects/descrobject.c:476:24 (python3.15t+0x2262d5)
#5 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x20c593)
#6 PyObject_Vectorcall /cpython/Objects/call.c:327:12 (python3.15t+0x20c593)
#7 _Py_VectorCallInstrumentation_StackRefSteal /cpython/Python/ceval.c:762:11 (python3.15t+0x422cbc)
#8 _PyEval_EvalFrameDefault /cpython/Python/generated_cases.c.h:1817:35 (python3.15t+0x428ce6)
#9 _PyEval_EvalFrame /cpython/./Include/internal/pycore_ceval.h:118:16 (python3.15t+0x422090)
#10 _PyEval_Vector /cpython/Python/ceval.c:2125:12 (python3.15t+0x422090)
#11 _PyFunction_Vectorcall /cpython/Objects/call.c (python3.15t+0x20cc0f)
#12 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x2112e6)
#13 method_vectorcall /cpython/Objects/classobject.c:74:20 (python3.15t+0x2112e6)
#14 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x476281)
#15 context_run /cpython/Python/context.c:727:29 (python3.15t+0x476281)
#16 method_vectorcall_FASTCALL_KEYWORDS /cpython/Objects/descrobject.c:421:24 (python3.15t+0x226017)
#17 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x20c593)
#18 PyObject_Vectorcall /cpython/Objects/call.c:327:12 (python3.15t+0x20c593)
#19 _Py_VectorCallInstrumentation_StackRefSteal /cpython/Python/ceval.c:762:11 (python3.15t+0x422cbc)
#20 _PyEval_EvalFrameDefault /cpython/Python/generated_cases.c.h:1817:35 (python3.15t+0x428ce6)
#21 _PyEval_EvalFrame /cpython/./Include/internal/pycore_ceval.h:118:16 (python3.15t+0x422090)
#22 _PyEval_Vector /cpython/Python/ceval.c:2125:12 (python3.15t+0x422090)
#23 _PyFunction_Vectorcall /cpython/Objects/call.c (python3.15t+0x20cc0f)
#24 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x2112e6)
#25 method_vectorcall /cpython/Objects/classobject.c:74:20 (python3.15t+0x2112e6)
#26 _PyVectorcall_Call /cpython/Objects/call.c:273:16 (python3.15t+0x20c89b)
#27 _PyObject_Call /cpython/Objects/call.c:348:16 (python3.15t+0x20c89b)
#28 PyObject_Call /cpython/Objects/call.c:373:12 (python3.15t+0x20c905)
#29 thread_run /cpython/./Modules/_threadmodule.c:387:21 (python3.15t+0x5f5512)
#30 pythread_wrapper /cpython/Python/thread_pthread.h:234:5 (python3.15t+0x526127)
Previous atomic write of size 8 at 0x7fffb60c01b0 by thread T2:
#0 _Py_atomic_store_ptr_release /cpython/./Include/cpython/pyatomic_gcc.h:565:3 (python3.15t+0x29435b)
#1 insertdict /cpython/Objects/dictobject.c (python3.15t+0x29435b)
#2 setitem_take2_lock_held /cpython/Objects/dictobject.c:2684:12 (python3.15t+0x2936a7)
#3 setitem_lock_held /cpython/Objects/dictobject.c:2721:12 (python3.15t+0x29ff83)
#4 _PyDict_SetItem_LockHeld /cpython/Objects/dictobject.c:6850:16 (python3.15t+0x29ff83)
#5 _PyObjectDict_SetItem /cpython/Objects/dictobject.c:7549:11 (python3.15t+0x2a3d97)
#6 _PyObject_GenericSetAttrWithDict /cpython/Objects/object.c:2055:19 (python3.15t+0x2cbf44)
#7 PyObject_GenericSetAttr /cpython/Objects/object.c:2083:12 (python3.15t+0x2cc697)
#8 PyObject_SetAttr /cpython/Objects/object.c:1528:15 (python3.15t+0x2c8f4f)
#9 builtin_setattr_impl /cpython/Python/bltinmodule.c:1744:9 (python3.15t+0x41d2e7)
#10 builtin_setattr /cpython/Python/clinic/bltinmodule.c.h:692:20 (python3.15t+0x41d2e7)
#11 cfunction_vectorcall_FASTCALL /cpython/Objects/methodobject.c:449:24 (python3.15t+0x2bbb1e)
#12 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x20c593)
#13 PyObject_Vectorcall /cpython/Objects/call.c:327:12 (python3.15t+0x20c593)
#14 _Py_VectorCallInstrumentation_StackRefSteal /cpython/Python/ceval.c:762:11 (python3.15t+0x422cbc)
#15 _PyEval_EvalFrameDefault /cpython/Python/generated_cases.c.h:1817:35 (python3.15t+0x428ce6)
#16 _PyEval_EvalFrame /cpython/./Include/internal/pycore_ceval.h:118:16 (python3.15t+0x422090)
#17 _PyEval_Vector /cpython/Python/ceval.c:2125:12 (python3.15t+0x422090)
#18 _PyFunction_Vectorcall /cpython/Objects/call.c (python3.15t+0x20cc0f)
#19 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x2112e6)
#20 method_vectorcall /cpython/Objects/classobject.c:74:20 (python3.15t+0x2112e6)
#21 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x476281)
#22 context_run /cpython/Python/context.c:727:29 (python3.15t+0x476281)
#23 method_vectorcall_FASTCALL_KEYWORDS /cpython/Objects/descrobject.c:421:24 (python3.15t+0x226017)
#24 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x20c593)
#25 PyObject_Vectorcall /cpython/Objects/call.c:327:12 (python3.15t+0x20c593)
#26 _Py_VectorCallInstrumentation_StackRefSteal /cpython/Python/ceval.c:762:11 (python3.15t+0x422cbc)
#27 _PyEval_EvalFrameDefault /cpython/Python/generated_cases.c.h:1817:35 (python3.15t+0x428ce6)
#28 _PyEval_EvalFrame /cpython/./Include/internal/pycore_ceval.h:118:16 (python3.15t+0x422090)
#29 _PyEval_Vector /cpython/Python/ceval.c:2125:12 (python3.15t+0x422090)
#30 _PyFunction_Vectorcall /cpython/Objects/call.c (python3.15t+0x20cc0f)
#31 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:136:11 (python3.15t+0x2112e6)
#32 method_vectorcall /cpython/Objects/classobject.c:74:20 (python3.15t+0x2112e6)
#33 _PyVectorcall_Call /cpython/Objects/call.c:273:16 (python3.15t+0x20c89b)
#34 _PyObject_Call /cpython/Objects/call.c:348:16 (python3.15t+0x20c89b)
#35 PyObject_Call /cpython/Objects/call.c:373:12 (python3.15t+0x20c905)
#36 thread_run /cpython/./Modules/_threadmodule.c:387:21 (python3.15t+0x5f5512)
#37 pythread_wrapper /cpython/Python/thread_pthread.h:234:5 (python3.15t+0x526127)
SUMMARY: ThreadSanitizer: data race /cpython/Objects/dictobject.c:3020:40 in _PyDict_Next
Version: Python 3.15.0a5+ free-threading build (heads/main:d5f96c86653, Feb 11 2026, 04:50:14) [Clang 18.1.3 (1ubuntu1)]
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux