segfault when deleting an object after returning it

[graingert]

a slightly minimized segfault:

import asyncio


async def asyncfn():
 pass

def create_task(loop, coro, **kwargs):
 task = asyncio.Task(coro, loop=loop, **kwargs)
 try:
 return task
 finally:
 # gh-128552: prevent a refcycle of
 # task.exception().__traceback__->BaseEventLoop.create_task->task
 del task

async def main():
 t = create_task(asyncio.get_running_loop(), asyncfn(), eager_start=True, name="example")
 assert t.done()
 await t

asyncio.run(main(), loop_factory=asyncio.EventLoop)

Originally posted by @graingert in #128306 (comment)

Linked PRs

• gh-133371: Don't optimize LOAD_FAST instructions whose local is killed by DELETE_FAST #133383

[efimov-mikhail]

I also have a segfault on this source code snippet.

Moreover, very simplified example like this

def create_obj():
 obj = [42]
 try:
 return obj
 finally:
 del obj

o = create_obj()
print(o)

also have a problem (assertion, not crash):

python: ./Include/internal/pycore_gc.h:167: _PyGCHead_SET_NEXT: Assertion `(unext & ~_PyGC_PREV_MASK) == 0' failed.
[1] 667990 IOT instruction ./python asyncio_segfault.py

Is it in general correct to delete returned object in finally section?

[graingert]

Is it in general correct to delete returned object in finally section?

Yes, this is correct