New submission from Kyle Stanley <[email protected]>:
When using the `test-with-buildbots` label in GH-19149 (which involved no C
changes), a failure occurred in test_asyncio for several of the refleak
buildbots. Here's the output of a few:
AMD64 Fedora Stable Refleaks PR:
test_asyncio leaked [3, 3, 27] references, sum=33
test_asyncio leaked [3, 3, 28] memory blocks, sum=34
2 tests failed again:
test__xxsubinterpreters test_asyncio
== Tests result: FAILURE then FAILURE ==
AMD64 RHEL8 Refleaks PR:
test_asyncio leaked [3, 3, 3] references, sum=9
test_asyncio leaked [3, 3, 3] memory blocks, sum=9
2 tests failed again:
test__xxsubinterpreters test_asyncio
== Tests result: FAILURE then FAILURE ==
RHEL7 Refleaks PR:
test_asyncio leaked [3, 3, 3] references, sum=9
test_asyncio leaked [3, 3, 3] memory blocks, sum=9
2 tests failed again:
test__xxsubinterpreters test_asyncio
== Tests result: FAILURE then FAILURE ==
I'm unable to replicate it locally, but I think I may have located a subtle,
uncommon refleak in `future_add_done_callback()`, within _asynciomodule.c.
Specifically:
```
PyObject *tup = PyTuple_New(2);
if (tup == NULL) {
return NULL;
}
Py_INCREF(arg);
PyTuple_SET_ITEM(tup, 0, arg);
Py_INCREF(ctx);
PyTuple_SET_ITEM(tup, 1, (PyObject *)ctx);
if (fut->fut_callbacks != NULL) {
int err = PyList_Append(fut->fut_callbacks, tup);
if (err) {
Py_DECREF(tup);
return NULL;
}
Py_DECREF(tup);
}
else {
fut->fut_callbacks = PyList_New(1);
if (fut->fut_callbacks == NULL) {
// Missing ``Py_DECREF(tup);`` ?
return NULL;
}
```
(The above code is located at:
https://github.com/python/cpython/blob/7668a8bc93c2bd573716d1bea0f52ea520502b28/Modules/_asynciomodule.c#L664-L685)
In the above conditional for "if (fut->fut_callbacks == NULL)", it appears that
`tup` is pointing to a non-NULL new reference at this point, and thus should be
decref'd prior to returning NULL. Otherwise, it seems like it could be leaked.
But, I would appreciate it if someone could double check this (the C-API isn't
an area I'm experienced); particularly since this code has been in place for a
decent while (since 3.7). I _suspect_ it's gone undetected and only failed
intermittently because this specific ``return NULL`` path is rather uncommon.
I'd be glad to open a PR to address the issue, assuming I'm not missing
something with the above refleak. Otherwise, feel free to correct me.
----------
assignee: aeros
components: C API, Extension Modules
messages: 364985
nosy: aeros, asvetlov, yselivanov
priority: high
severity: normal
status: open
title: Possible refleak in _asynciomodule.c future_add_done_callback()
type: resource usage
versions: Python 3.7, Python 3.8, Python 3.9
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<https://bugs.python.org/issue40061>
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