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GH-133261: Make sure that the GC doesn't untrack objects in trashcan (GH-133431)

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Mark Shannon 2025-05-05 13:44:50 +01:00 • committed by GitHub
parent 8d5f3cd2ce
commit f554237b8e
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3 changed files with 36 additions and 6 deletions
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38
Objects/object.c
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@ -2930,6 +2930,33 @@ finally:
/* Trashcan support. */
#ifndef Py_GIL_DISABLED
/* We need to store a pointer in the refcount field of
* an object. It is important that we never store 0 (NULL).
* It is also important to not make the object appear immortal,
* or it might be untracked by the cycle GC. */
static uintptr_t
pointer_to_safe_refcount(void *ptr)
{
uintptr_t full = (uintptr_t)ptr;
assert((full & 3) == 0);
uint32_t refcnt = (uint32_t)full;
if (refcnt >= (uint32_t)_Py_IMMORTAL_MINIMUM_REFCNT) {
full = full - ((uintptr_t)_Py_IMMORTAL_MINIMUM_REFCNT) + 1;
}
return full + 2;
}
static void *
safe_refcount_to_pointer(uintptr_t refcnt)
{
if (refcnt & 1) {
refcnt += _Py_IMMORTAL_MINIMUM_REFCNT - 1;
}
return (void *)(refcnt - 2);
}
#endif
/* Add op to the gcstate->trash_delete_later list. Called when the current
* call-stack depth gets large. op must be a currently untracked gc'ed
* object, with refcount 0. Py_DECREF must already have been called on it.
@ -2941,11 +2968,10 @@ _PyTrash_thread_deposit_object(PyThreadState *tstate, PyObject *op)
#ifdef Py_GIL_DISABLED
op->ob_tid = (uintptr_t)tstate->delete_later;
#else
/* Store the delete_later pointer in the refcnt field.
* As this object may still be tracked by the GC,
* it is important that we never store 0 (NULL). */
uintptr_t refcnt = (uintptr_t)tstate->delete_later;
*((uintptr_t*)op) = refcnt+1;
/* Store the delete_later pointer in the refcnt field. */
uintptr_t refcnt = pointer_to_safe_refcount(tstate->delete_later);
*((uintptr_t*)op) = refcnt;
assert(!_Py_IsImmortal(op));
#endif
tstate->delete_later = op;
}
@ -2967,7 +2993,7 @@ _PyTrash_thread_destroy_chain(PyThreadState *tstate)
/* Get the delete_later pointer from the refcnt field.
* See _PyTrash_thread_deposit_object(). */
uintptr_t refcnt = *((uintptr_t*)op);
tstate->delete_later = (PyObject *)(refcnt - 1);
tstate->delete_later = safe_refcount_to_pointer(refcnt);
op->ob_refcnt = 0;
#endif