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Data race in the codec.errors setter (codecctx_errors_set) on a shared stateful codec #152767
Description
Bug report
Bug description:
Bug description:
In the free-threaded build, the codecctx_errors_set decrefs the old handler(ERROR_DECREF(self->errors)) and stores the new one (self->errors = cb) without any synchronization
cpython/Modules/cjkcodecs/multibytecodec.c
Lines 170 to 197 in ecdef17
For any handler name other than the strict/ignore/replace sentinels (e.g. backslashreplace), self->errors holds a real refcounted PyUnicode.
The decref-then-assign is not atomic, so concurrent codec.errors = drops references incorrectly and can free a handler while it is still referenced.
Reproducer:
import codecs
import random
from threading import Thread
shared = codecs.getincrementalencoder('shift_jis')()
NAMES = ['backslashreplace', 'xmlcharrefreplace', 'namereplace']
def thread1():
for _ in range(20000):
try:
shared.errors = random.choice(NAMES)
except Exception:
pass
if __name__ == "__main__":
threads = [Thread(target=thread1) for _ in range(8)]
for t in threads: t.start()
for t in threads: t.join()TSAN Report:
==================
WARNING: ThreadSanitizer: data race (pid=3576762)
Read of size 8 at 0x7fffb65a1cc0 by thread T2:
#0 codecctx_errors_set /cpython/./Modules/cjkcodecs/multibytecodec.c:194:5
#1 getset_set /cpython/Objects/descrobject.c:250:16
#2 _PyObject_GenericSetAttrWithDict /cpython/Objects/object.c:2049:19
#3 PyObject_GenericSetAttr /cpython/Objects/object.c:2120:12
#4 PyObject_SetAttr /cpython/Objects/object.c:1533:15
#5 _PyEval_EvalFrameDefault /cpython/Python/generated_cases.c.h:12146:27
...
Previous write of size 8 at 0x7fffb65a1cc0 by thread T1:
#0 codecctx_errors_set /cpython/./Modules/cjkcodecs/multibytecodec.c:195:18
#1 getset_set /cpython/Objects/descrobject.c:250:16
#2 _PyObject_GenericSetAttrWithDict /cpython/Objects/object.c:2049:19
#3 PyObject_GenericSetAttr /cpython/Objects/object.c:2120:12
#4 PyObject_SetAttr /cpython/Objects/object.c:1533:15
#5 _PyEval_EvalFrameDefault /cpython/Python/generated_cases.c.h:12146:27
...
SUMMARY: ThreadSanitizer: data race /cpython/./Modules/cjkcodecs/multibytecodec.c:194:5 in codecctx_errors_set
==================
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
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