test_pyobject_is_freed_free fails with 3.8.0beta1

[mcepl]

BPO	37169
Nosy	@vstinner, @mcepl
PRs	bpo-37169: Rewrite _PyObject_IsFreed() unit tests #13888 [3.8] bpo-37169: Rewrite _PyObject_IsFreed() unit tests (GH-13888) #13895
Files	log.txt.gz is_freed.py log.txt.gz

^{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 2019-06-07.15:57:37.288>
created_at = <Date 2019-06-05.23:51:51.498>
labels = ['interpreter-core', '3.8', '3.9']
title = 'test_pyobject_is_freed_free fails with 3.8.0beta1'
updated_at = <Date 2019-06-21.19:09:02.768>
user = 'https://github.com/mcepl'

bugs.python.org fields:

activity = <Date 2019-06-21.19:09:02.768>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-07.15:57:37.288>
closer = 'vstinner'
components = ['Interpreter Core']
creation = <Date 2019-06-05.23:51:51.498>
creator = 'mcepl'
dependencies = []
files = ['48397', '48398', '48431']
hgrepos = []
issue_num = 37169
keywords = ['patch']
message_count = 12.0
messages = ['344782', '344807', '344820', '344821', '344822', '344823', '344824', '344942', '344954', '344956', '346214', '346244']
nosy_count = 2.0
nosy_names = ['vstinner', 'mcepl']
pr_nums = ['13888', '13895']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue37169'
versions = ['Python 3.8', 'Python 3.9']

[mcepl]

When building openSUSE package for Python-3.8.0b1 (on x86_64 build system with the latest openSUSE/Tumbleweed) in the package which previously worked all the way up to 3.8.0.a4, I get this test failing:

[ 5771s] ======================================================================
[ 5771s] FAIL: test_pyobject_is_freed_free (test.test_capi.PyMemMallocDebugTests)
[ 5771s] ----------------------------------------------------------------------

[ 5771s] Traceback (most recent call last):
[ 5771s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/test_capi.py", line 729, in test_pyobject_is_freed_free
[ 5771s]     self.check_pyobject_is_freed('pyobject_freed')
[ 5771s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/test_capi.py", line 720, in check_pyobject_is_freed
[ 5771s]     assert_python_ok('-c', code, PYTHONMALLOC=self.PYTHONMALLOC)
[ 5771s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/support/script_helper.py", line 157, in assert_python_ok
[ 5771s]     return _assert_python(True, *args, **env_vars)
[ 5771s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/support/script_helper.py", line 143, in _assert_python
[ 5771s]     res.fail(cmd_line)
[ 5771s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/support/script_helper.py", line 70, in fail
[ 5771s]     raise AssertionError("Process return code is %d\n"
[ 5771s] AssertionError: Process return code is 1
[ 5771s] command line: ['/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/python', '-X', 'faulthandler', '-c', '\nimport gc, os, sys, _testcapi\n# Disable the GC to avoid crash on GC collection\ngc.disable()\nobj = _testcapi.pyobject_freed()\nerror = (_testcapi.pyobject_is_freed(obj) == False)\n# Exit immediately to avoid a crash while deallocating\n# the invalid object\nos._exit(int(error))\n']
[ 5771s] 
[ 5771s] stdout:
[ 5771s] 

---

[ 5771s]
[ 5771s] ---
[ 5771s]
[ 5771s] stderr:
[ 5771s] ---
[ 5771s]
[ 5771s] ---
[ 5771s]
[ 5771s] ----------------------------------------------------------------------

[vstinner]

When building openSUSE package for Python-3.8.0b1 (on x86_64 build system with the latest openSUSE/Tumbleweed)

How do you build Python?

• configure command
• C compiler
• etc.

[mcepl]

Complete build log which shows all dependent libraries, compilation options, etc. If you want any other artifacts (config.log, Python.h) just let me know.

[vstinner]

Matej provides me a link to the build logs on IRC:

It's GCC 9.1.1 (gcc9-9.1.1+r271393-1.2)

The compilation uses PGO and LTO.

./configure --host=x86_64-suse-linux-gnu --build=x86_64-suse-linux-gnu --program-prefix= --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64 --libexecdir=/usr/lib --localstatedir=/var --sharedstatedir=/var/lib --mandir=/usr/share/man --infodir=/usr/share/info --disable-dependency-tracking --docdir=/usr/share/doc/packages/python --enable-ipv6 --enable-shared --with-ensurepip=no --with-system-ffi --with-system-expat --with-lto --enable-optimizations --enable-loadable-sqlite-extensions

[ 44s] configure: WARNING: unrecognized options: --disable-dependency-tracking, --disable-dependency-tracking

--

I'm unable to reproduce the issue on Fedora 30 using GCC 9.1.1:

$ ./configure --host=x86_64-suse-linux-gnu --build=x86_64-suse-linux-gnu --program-prefix= --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64 --libexecdir=/usr/lib --localstatedir=/var --sharedstatedir=/var/lib --mandir=/usr/share/man --infodir=/usr/share/info --disable-dependency-tracking --docdir=/usr/share/doc/packages/python --enable-ipv6 --enable-shared --with-ensurepip=no --with-system-ffi --with-system-expat --with-lto --enable-optimizations --enable-loadable-sqlite-extensions
...
$ vim Makefile
# replace "PROFILE_TASK=..." with "PROFILE_TASK=-c pass", just to make compilation faster ;-)
$ make
...
$ LD_LIBRARY_PATH=$PWD ./python -m test -v test_capi
...
Tests result: SUCCESS

[vstinner]

test_pyobject_is_freed_free() test can be simplified as attached is_freed.py using:

$ LD_LIBRARY_PATH=$PWD PYTHONMALLOC=debug ./python is_freed.py; echo $?
0

0 means success: the test pass.

1 means failure: the test fails.

(Again, I cannot reproduce this failure.)

[vstinner]

Oh wait, only PyMemMallocDebugTests fails:

class PyMemMallocDebugTests(PyMemDebugTests):
    PYTHONMALLOC = 'malloc_debug'

Logs:

[ 2863s] test_pyobject_is_freed_free (test.test_capi.PyMemDebugTests) ... ok
[ 2863s] test_pyobject_is_freed_free (test.test_capi.PyMemDefaultTests) ... skipped 'need Py_DEBUG'
[ 2863s] test_pyobject_is_freed_free (test.test_capi.PyMemMallocDebugTests) ... FAIL
[ 2863s] test_pyobject_is_freed_free (test.test_capi.PyMemPymallocDebugTests) ... ok

So the correct line to reproduce the bug should be:

$ LD_LIBRARY_PATH=$PWD PYTHONMALLOC=malloc_debug ./python is_freed.py; echo $?
0

[vstinner]

I designed unit tests to be optimistic: expect that freed memory will be untouched during a few Python instructions:

# create an object, free its memory
obj = _testcapi.pyobject_freed()
# check that the object memory is freed
error = (_testcapi.pyobject_is_freed(obj) == False)

Maybe calling _testcapi.pyobject_is_freed() reuse the memory which has just been freed.

The test should be fully ritten in C to avoid this issue.

I wrote the test using 2 Python functions just to make the test simpler to write, but it seems like *sometimes*, it can fail.

[vstinner]

New changeset 3bf0f3a by Victor Stinner in branch 'master':
bpo-37169: Rewrite _PyObject_IsFreed() unit tests (GH-13888)
3bf0f3a

[vstinner]

New changeset 3576266 by Victor Stinner in branch '3.8':
bpo-37169: Rewrite _PyObject_IsFreed() unit tests (GH-13888) (GH-13895)
3576266

[vstinner]

Matej Cepl: thanks for the bug report, it should now be fixed.

[mcepl]

I don't think this has been really fixed, see attached log,even with the patch applied I am still getting:

[ 6220s] ======================================================================
[ 6220s] FAIL: test_pyobject_freed_is_freed (test.test_capi.PyMemMallocDebugTests)
[ 6220s] ----------------------------------------------------------------------

[ 6220s] Traceback (most recent call last):
[ 6220s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/test_capi.py", line 730, i
n test_pyobject_freed_is_freed
[ 6220s]     self.check_pyobject_is_freed('check_pyobject_freed_is_freed')
[ 6220s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/test_capi.py", line 721, i
n check_pyobject_is_freed
[ 6220s]     assert_python_ok('-c', code, PYTHONMALLOC=self.PYTHONMALLOC)
[ 6220s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/support/script_helper.py",
 line 157, in assert_python_ok
[ 6220s]     return _assert_python(True, *args, **env_vars)
[ 6220s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/support/script_helper.py",
 line 143, in _assert_python
[ 6220s]     res.fail(cmd_line)
[ 6220s]   File "/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/Lib/test/support/script_helper.py", line 70, in fail
[ 6220s]     raise AssertionError("Process return code is %d\n"
[ 6220s] AssertionError: Process return code is 1
[ 6220s] command line: ['/home/abuild/rpmbuild/BUILD/Python-3.8.0b1/python', '-X', 'faulthandler', '-c', '\nimport gc, os, sys, _testcapi\n# Disable the GC to avoid crash on GC collection\ngc.disable()\ntry:\n    _testcapi.check_pyobject_freed_is_freed()\n    # Exit immediately to avoid a crash while deallocating\n    # the invalid object\n    os._exit(0)\nexcept _testcapi.error:\n    os._exit(1)\n']