[issue26797] Segafault in _PyObject_Alloc

[STINNER Victor]

STINNER Victor added the comment:

> Closing this one. Haven't seen this in a while, probably it was a bug in 
> libuv.

I told you so! :-D

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[issue26797] Segafault in _PyObject_Alloc

[Yury Selivanov]

Yury Selivanov added the comment:

Closing this one. Haven't seen this in a while, probably it was a bug in libuv.

--
resolution:  -> works for me
stage: test needed -> resolved
status: open -> closed

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[issue26797] Segafault in _PyObject_Alloc

[STINNER Victor]

STINNER Victor added the comment:

Usually a "bug in the memory allocator" means a buffer overflow in your
code. Did you check your code using a debug build, PYTHONDEBUG=debug (if
CPython is compiled in release mode), or PYTHONMALLOC=malloc + valgrind?
(The env var requires CPython 3.6)

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[issue26797] Segafault in _PyObject_Alloc

[Ned Deily]

Changes by Ned Deily :


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nosy: +ronaldoussoren

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[issue26797] Segafault in _PyObject_Alloc

[Yury Selivanov]

New submission from Yury Selivanov:

I'm working on an implementation of asyncio event loop on top of libuv [1].  
One of my tests crashes on Mac OS X with a segfault [2].  The problem is that 
it's not consistent -- looks like it depends on size of uvloop so binary, 
or/and amount of objects allocated in program.

I can't reproduce the problem on a debug build, or write a test for it, it is 
really a weird edge-case.  But I'm certain that we have a bug in our memory 
allocator.

Here's a screenshot of crash log [3], and here's an lldb disassembly of crash 
location [4].

Now, what's going on in [2] is:
1. uvloop sets a sigint signal handler the moment it starts the loop
2. uvloop start to execute a coroutine, which blocks on a long "time.sleep(..)" 
call
3. sigint handler receives a SIGINT and calls PyErr_SetInterrupt
4. CPython interrupts the code, KeyboardInterrupt is instantiated and raised
5. CPython starts to render the traceback to print it to stderr, and this is 
where it tries to allocate some object, and this is where we hit a bad-access 
in _PyObject_Alloc.

I'd really appreciate any ideas on what's going on here and how we can fix this.


[1] https://github.com/magicstack/uvloop
[2] https://github.com/MagicStack/uvloop/blob/v0.4.6/tests/test_signals.py#L14
[3] http://imgur.com/6GcE92X
[4] https://gist.github.com/1st1/b46f3702aeb1b57fe4ad32b19ed63c3f

--
messages: 263678
nosy: haypo, ned.deily, serhiy.storchaka, yselivanov
priority: normal
severity: normal
stage: test needed
status: open
title: Segafault in _PyObject_Alloc
type: crash
versions: Python 3.5

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