pythongh-105987: Fix reference counting issue in _asyncio._swap_current_task (python#105989)

Author: chgnrdv

Lib/test/test_asyncio/test_eager_task_factory.py

@@ -7,6 +7,8 @@
 from unittest import mock
 from asyncio import tasks
 from test.test_asyncio import utils as test_utils
+import test.support
+from test.support.script_helper import assert_python_ok
 
 MOCK_ANY = mock.ANY
 
@@ -222,6 +224,23 @@ class PyEagerTaskFactoryLoopTests(EagerTaskFactoryLoopTests, test_utils.TestCase
 class CEagerTaskFactoryLoopTests(EagerTaskFactoryLoopTests, test_utils.TestCase):
  Task = getattr(tasks, '_CTask', None)
 
+ def test_issue105987(self):
+ code = """if 1:
+ from _asyncio import _swap_current_task
+
+ class DummyTask:
+ pass
+
+ class DummyLoop:
+ pass
+
+ l = DummyLoop()
+ _swap_current_task(l, DummyTask())
+ t = _swap_current_task(l, None)
+ """
+
+ _, out, err = assert_python_ok("-c", code)
+ self.assertFalse(err)
 
 class AsyncTaskCounter:
  def __init__(self, loop, *, task_class, eager):

Misc/NEWS.d/next/Library/2023-06-22-15-21-11.gh-issue-105987.T7Kzrb.rst

@@ -0,0 +1 @@
+Fix crash due to improper reference counting in :mod:`asyncio` eager task factory internal routines.

Modules/_asynciomodule.c

@@ -2047,20 +2047,23 @@ swap_current_task(asyncio_state *state, PyObject *loop, PyObject *task)
  }
  prev_task = Py_None;
  }
+ Py_INCREF(prev_task);
 
  if (task == Py_None) {
  if (_PyDict_DelItem_KnownHash(state->current_tasks, loop, hash) == -1) {
- return NULL;
+ goto error;
  }
  } else {
  if (_PyDict_SetItem_KnownHash(state->current_tasks, loop, task, hash) == -1) {
- return NULL;
+ goto error;
  }
  }
 
- Py_INCREF(prev_task);
-
  return prev_task;
+
+error:
+ Py_DECREF(prev_task);
+ return NULL;
 }
 
 /* ----- Task */