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gh-145376: Fix reference leaks in _collectionsmodule.c #145421

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Merged
vstinner merged 1 commit into from
Mar 4, 2026
+6 −3
Merged

gh-145376: Fix reference leaks in _collectionsmodule.c #145421

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9 changes: 6 additions & 3 deletions Modules/_collectionsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -342,8 +342,10 @@ deque_append_lock_held(dequeobject *deque, PyObject *item, Py_ssize_t maxlen)
{
if (deque->rightindex == BLOCKLEN - 1) {
block *b = newblock(deque);
if (b == NULL)
if (b == NULL) {
Py_DECREF(item);
return -1;
}
b->leftlink = deque->rightblock;
CHECK_END(deque->rightblock->rightlink);
deque->rightblock->rightlink = b;
Expand Down Expand Up @@ -389,8 +391,10 @@ deque_appendleft_lock_held(dequeobject *deque, PyObject *item,
{
if (deque->leftindex == 0) {
block *b = newblock(deque);
if (b == NULL)
if (b == NULL) {
Py_DECREF(item);
return -1;
}
b->rightlink = deque->leftblock;
CHECK_END(deque->leftblock->leftlink);
deque->leftblock->leftlink = b;
Expand Down Expand Up @@ -564,7 +568,6 @@ deque_extendleft_impl(dequeobject *deque, PyObject *iterable)
iternext = *Py_TYPE(it)->tp_iternext;
while ((item = iternext(it)) != NULL) {
if (deque_appendleft_lock_held(deque, item, maxlen) == -1) {
Py_DECREF(item);
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@sergey-miryanov sergey-miryanov Mar 4, 2026

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iternext returns a new reference. Should we leave this line unchanged?

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@encukou encukou Mar 4, 2026

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I agree, this is fishy. Does deque_append[left]_lock_held steal item, or not?

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@vstinner vstinner Mar 4, 2026

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With this change, deque_appendleft_lock_held() always steal its item argument. So removing Py_DECREF(item) here is correct.

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@eendebakpt eendebakpt Mar 4, 2026

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The deque_appendleft_lock_held indeed steals the second argument reference. I wrote this in the OP, but did not add a comment in the code.
If you agree, I will add a comment to the start of deque_append_lock_held/deque_appendleft_lock_held.

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@sergey-miryanov sergey-miryanov Mar 4, 2026

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I see now, thanks!
Maybe it is worth to add a comment, that deque_appendleft_lock_held steals reference to the second argument?

Py_DECREF(it);
return NULL;
}
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