Segmentation fault in asyncio

[akayunov]

BPO	38785
Nosy	@vstinner, @asvetlov, @1st1, @miss-islington, @akayunov
PRs	bpo-38785: Prevent asyncio from crashing  #17144 [3.8] bpo-38785: Prevent asyncio from crashing (GH-17144) #17147 [3.7] bpo-38785: Prevent asyncio from crashing (GH-17144) #17148
Files	scratch_15.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-11-13.21:55:19.610>
created_at = <Date 2019-11-13.08:34:09.900>
labels = ['3.7', '3.8', '3.9', 'type-crash', 'expert-asyncio']
title = 'Segmentation fault in asyncio'
updated_at = <Date 2019-11-13.21:55:19.604>
user = 'https://github.com/akayunov'

bugs.python.org fields:

activity = <Date 2019-11-13.21:55:19.604>
actor = 'asvetlov'
assignee = 'none'
closed = True
closed_date = <Date 2019-11-13.21:55:19.610>
closer = 'asvetlov'
components = ['asyncio']
creation = <Date 2019-11-13.08:34:09.900>
creator = 'akayunov'
dependencies = []
files = ['48712']
hgrepos = []
issue_num = 38785
keywords = ['patch']
message_count = 8.0
messages = ['356523', '356524', '356526', '356527', '356528', '356557', '356559', '356560']
nosy_count = 5.0
nosy_names = ['vstinner', 'asvetlov', 'yselivanov', 'miss-islington', 'akayunov']
pr_nums = ['17144', '17147', '17148']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue38785'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[akayunov]

Get Segmentation fault on run script in attachment.

[akayunov]

Get seg fault on running script in attachment:

root@fake:/opt/securisync/be# python3.7 scratch_15.py
In tratata before
In tratata2 before
Segmentation fault

[asvetlov]

Thanks for the report!
I would say that deriving from the future class without calling super().__init__() is an error.
After fixing this the snippet raises expected "RuntimeError: yield was used instead of yield from in task" error.

[vstinner]

The crash occurs in _asyncio_Future_get_loop():

(gdb) frame
#0 0x00007fffea2fe689 in _Py_INCREF (op=0x0) at ./Include/object.h:459
459 op->ob_refcnt++;

(gdb) up
#1 0x00007fffea301b14 in _asyncio_Future_get_loop_impl (self=0x7fffea2615f0)
at /home/vstinner/python/master/Modules/_asynciomodule.c:1094
1094 Py_INCREF(self->fut_loop);

(gdb) p self->fut_loop
$1 = 0x0

(gdb) where
#0 0x00007fffea2fe689 in _Py_INCREF (op=0x0) at ./Include/object.h:459
#1 0x00007fffea301b14 in _asyncio_Future_get_loop_impl (self=0x7fffea2615f0)
at /home/vstinner/python/master/Modules/_asynciomodule.c:1094
#2 0x00007fffea2fef01 in _asyncio_Future_get_loop (self=0x7fffea2615f0,
_unused_ignored=0x0)
at /home/vstinner/python/master/Modules/clinic/_asynciomodule.c.h:252
#3 0x0000000000645364 in cfunction_vectorcall_NOARGS (
func=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>,
args=0x0, nargsf=0, kwnames=0x0) at Objects/methodobject.c:424
#4 0x000000000042f8d1 in _PyObject_VectorcallTstate (tstate=0x81ae00,
callable=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>, args=0x0, nargsf=0, kwnames=0x0) at ./Include/cpython/abstract.h:111
#5 0x000000000042f930 in _PyObject_Vectorcall (
callable=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>, args=0x0, nargsf=0, kwnames=0x0) at ./Include/cpython/abstract.h:120
#6 0x000000000042f988 in _PyObject_CallNoArg (
func=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>)
at ./Include/cpython/abstract.h:148
#7 0x000000000042fc57 in PyObject_CallNoArgs (
func=<built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>)
at Objects/call.c:83
#8 0x00007fffea2ffc16 in get_future_loop (
fut=<Qwe2(value=0) at remote 0x7fffea2615f0>)
--Type <RET> for more, q to quit, c to continue without paging--q
Quit

(gdb) py-bt
Traceback (most recent call first):
  <built-in method get_loop of Qwe2 object at remote 0x7fffea2615f0>
  <built-in method run of Context object at remote 0x7fffea215170>
  File "/home/vstinner/python/master/Lib/asyncio/events.py", line 81, in _run
    self._context.run(self._callback, *self._args)
  File "/home/vstinner/python/master/Lib/asyncio/base_events.py", line 2641, in _run_once
  File "/home/vstinner/python/master/Lib/asyncio/base_events.py", line 1101, in run_forever
    await waiter
  File "/home/vstinner/python/master/Lib/asyncio/base_events.py", line 621, in run_until_complete
    self.run_forever()
  File "/home/vstinner/python/master/Lib/asyncio/runners.py", line 299, in run
  File "/home/vstinner/python/master/scratch_15.py", line 56, in <module>
    asyncio.run(main())

[asvetlov]

Looks like get_future_loop() function misses ENSURE_FUTURE_ALIVE macro call.

[miss-islington]

New changeset dad6be5 by Miss Islington (bot) (Andrew Svetlov) in branch 'master':
bpo-38785: Prevent asyncio from crashing (GH-17144)
dad6be5

[miss-islington]

New changeset 87b4d39 by Miss Islington (bot) in branch '3.7':
bpo-38785: Prevent asyncio from crashing (GH-17144)
87b4d39

[miss-islington]

New changeset 694c03f by Miss Islington (bot) in branch '3.8':
bpo-38785: Prevent asyncio from crashing (GH-17144)
694c03f