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[3.9] bpo-46070: _PyGC_Fini() untracks objects (GH-30577) #30580

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Merged
vstinner merged 1 commit into from
Jan 13, 2022
Merged

[3.9] bpo-46070: _PyGC_Fini() untracks objects (GH-30577) #30580

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bpo-46070: _PyGC_Fini() untracks objects (GH-30577) 
Py_EndInterpreter() now explicitly untracks all objects currently
tracked by the GC. Previously, if an object was used later by another
interpreter, calling PyObject_GC_UnTrack() on the object crashed if
the previous or the next object of the PyGC_Head structure became a
dangling pointer.

(cherry picked from commit 1a4d1c1)
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@vstinner
vstinner committed Jan 13, 2022
commit 2cc9e388629372e53ab9b8ed48714ac5528f0480
5 changes: 5 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2022-01-13-17-58-56.bpo-46070.q8IGth.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
:c:func:`Py_EndInterpreter` now explicitly untracks all objects currently
tracked by the GC. Previously, if an object was used later by another
interpreter, calling :c:func:`PyObject_GC_UnTrack` on the object crashed if the
previous or the next object of the :c:type:`PyGC_Head` structure became a
dangling pointer. Patch by Victor Stinner.
24 changes: 24 additions & 0 deletions Modules/gcmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2149,12 +2149,36 @@ _PyGC_DumpShutdownStats(PyThreadState *tstate)
}
}


static void
gc_fini_untrack(PyGC_Head *list)
{
PyGC_Head *gc;
for (gc = GC_NEXT(list); gc != list; gc = GC_NEXT(list)) {
PyObject *op = FROM_GC(gc);
_PyObject_GC_UNTRACK(op);
}
}


void
_PyGC_Fini(PyThreadState *tstate)
{
GCState *gcstate = &tstate->interp->gc;
Py_CLEAR(gcstate->garbage);
Py_CLEAR(gcstate->callbacks);

if (!_Py_IsMainInterpreter(tstate)) {
// bpo-46070: Explicitly untrack all objects currently tracked by the
// GC. Otherwise, if an object is used later by another interpreter,
// calling PyObject_GC_UnTrack() on the object crashs if the previous
// or the next object of the PyGC_Head structure became a dangling
// pointer.
for (int i = 0; i < NUM_GENERATIONS; i++) {
PyGC_Head *gen = GEN_HEAD(gcstate, i);
gc_fini_untrack(gen);
}
}
}

/* for debugging */
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