[3.12] gh-122527: Fix a crash on deallocation of PyStructSequence (GH-122577)
#122626
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…nce` (pythonGH-122577) The `PyStructSequence` destructor would crash if it was deallocated after its type's dictionary was cleared by the GC, because it couldn't compute the "real size" of the instance. This could occur with relatively straightforward code in the free-threaded build or with a reference cycle involving the type in the default build, due to differing orders in which `tp_clear()` was called. Account for the non-sequence fields in `tp_basicsize` and use that, along with `Py_SIZE()`, to compute the "real" size of a `PyStructSequence` in the dealloc function. This avoids the accesses to the type's dictionary during dealloc, which were unsafe. (cherry picked from commit 4b63cd1) Co-authored-by: Sam Gross <[email protected]>
This was referenced Aug 2, 2024
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serhiy-storchaka
approved these changes
Aug 12, 2024
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The
PyStructSequencedestructor would crash if it was deallocated after its type's dictionary was cleared by the GC, because it couldn't compute the "real size" of the instance. This could occur with relatively straightforward code in the free-threaded build or with a reference cycle involving the type in the default build, due to differing orders in whichtp_clear()was called.Account for the non-sequence fields in
tp_basicsizeand use that, along withPy_SIZE(), to compute the "real" size of aPyStructSequencein the dealloc function. This avoids the accesses to the type's dictionary during dealloc, which were unsafe. (cherry picked from commit 4b63cd1)