Bug: Reference leak in _asyncio_Task___init___impl in _asynciomodule.c

[Nico-Posada]

Bug report

Bug description:

I discovered this while working on #126080. If the func is given a context that isn't None, instead of doing Py_XSETREF it'll just do a regular assignment meaning that whatever was there before wont have its reference count decreased.

cpython/Modules/_asynciomodule.c

Lines 2122 to 2124 in 2544159

	} else {
	self->task_context = Py_NewRef(context);
	}

import asyncio
import sys

# for convenience so I dont have to set up everything else for a Task obj
# and can just focus on the ref leak
class Break:
    def __str__(self):
        raise Exception("break")

async def coro():
    pass

task = asyncio.Task.__new__(asyncio.Task)
co = coro()

obj = object()
print("refcount before bug", sys.getrefcount(obj))

for _ in range(10000):
    try:
        task.__init__(co, context=obj, name=Break())
    except: pass

print("refcount after bug", sys.getrefcount(obj))

Output

refcount before bug 2
refcount after bug 10002

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-126083: Fix a reference leak in asyncio.Task when reinitializing with new non-None context #126103
• [3.13] gh-126083: Fix a reference leak in asyncio.Task when reinitializing with new non-None context (GH-126103) #126229
• [3.12] gh-126083: Fix a reference leak in asyncio.Task when reinitializing with new non-None context (GH-126103) #126230

[sobolevn]

Yes, Py_XSETREF seems like a good solution here. @Nico-Posada, please send a PR :)