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gh-129069: Fix listobject.c data races due to memmove#142957
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The use of memmove and _Py_memory_repeat were not thread-safe in thefree threading build in some cases. In theory, memmove and_Py_memory_repeat can copy byte-by-byte instead of pointer-by-pointer,so concurrent readers could see uninitialized data or tearing.Additionally, we should be using "release" (or stronger) ordering to becompliant with the C11 memory model when copying objects within a list.
bedevere-bot commentedDec 18, 2025
🤖 New build scheduled with the buildbot fleet by@colesbury for commit97e8d13 🤖 Results will be shown at: https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F142957%2Fmerge If you want to schedule another build, you need to add the🔨 test-with-refleak-buildbots label again. |
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The use of memmove and _Py_memory_repeat were not thread-safe in the free threading build in some cases. In theory, memmove and _Py_memory_repeat can copy byte-by-byte instead of pointer-by-pointer, so concurrent readers could see uninitialized data or tearing.
Additionally, we should be using "release" (or stronger) ordering to be compliant with the C11 memory model when copying objects within a list.
I've also updated
list_resizeso it definitively doesn't fail when shrinking a list. This simplifies some of the call sites.