Undetected error in exception handling

[theller]

BPO	2548
Nosy	@warsaw, @brettcannon, @theller, @amauryfa, @pitrou, @devdanzin, @benjaminp
Files	excrecurse.patch

^{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 2010-08-16.21:38:15.544>
created_at = <Date 2008-04-04.08:16:41.003>
labels = ['interpreter-core', 'type-crash']
title = 'Undetected error in exception handling'
updated_at = <Date 2010-08-16.21:38:15.543>
user = 'https://github.com/theller'

bugs.python.org fields:

activity = <Date 2010-08-16.21:38:15.543>
actor = 'BreamoreBoy'
assignee = 'none'
closed = True
closed_date = <Date 2010-08-16.21:38:15.544>
closer = 'BreamoreBoy'
components = ['Interpreter Core']
creation = <Date 2008-04-04.08:16:41.003>
creator = 'theller'
dependencies = []
files = ['11314']
hgrepos = []
issue_num = 2548
keywords = ['patch', 'needs review']
message_count = 18.0
messages = ['64920', '64954', '64961', '64983', '65053', '66398', '68018', '70482', '71095', '71107', '71651', '72163', '72176', '72179', '72181', '101353', '110185', '110215']
nosy_count = 10.0
nosy_names = ['barry', 'nnorwitz', 'brett.cannon', 'theller', 'jafo', 'amaury.forgeotdarc', 'pitrou', 'ajaksu2', 'benjamin.peterson', 'BreamoreBoy']
pr_nums = []
priority = 'critical'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue2548'
versions = ['Python 2.6']

[theller]

[Found by Daniel Diniz (ajaksu2), see issue bpo-2542]

The following code triggers an undetected error with a debug build:

"""
import sys
def g():
try:
return g()
except:
return sys.exc_info()
g()
print 42
"""

Running the code prints this:

C:\svn\trunk\PCbuild>python_d test2.py
42
XXX undetected error
Traceback (most recent call last):
  File "test2.py", line 8, in <module>
    print 42
RuntimeError: maximum recursion depth exceeded
[8826 refs]

C:\svn\trunk\PCbuild>

[amauryfa]

Analysis: the primary recursion error is correctly raised, but then
there is a call to PyErr_NormalizeException, which calls
PyEval_CallObject, which increases the stack depth and hit the recursion
limit again...
python2.5 don't have the problem because PyEval_CallObject did not check
the recursion limit.

Different solutions I can think of:

• use a prebuilt exception: not possible if we still want an error
  message containing the context.
• in PyErr_NormalizeException, "PyEval_CallObject" is too generic. We
  could have a special path for exception types deriving from
  BaseException: directly call the constructor.

[nnorwitz]

Brett, didn't you have a similar problem you fixed a while ago? I
assigned to you for more input, feel free to reset to nobody.

[brettcannon]

Neal has the memory of an elephant or something.

Yes, I dealt with a similar issue where the recursion limit was hit, but
then normalizing the exception just caused it to hit it again. I thought
I changed it such that normalizing an exception actually turned off the
depth check or to raise a pre-defined exception for the recursion depth
limit.

I don't have time to look at this right now (still on holiday in
Brussels), but if I remember correctly the last time this came up I
liked the pre-allocated recursion limit exception.

[devdanzin]

I've identified rev58032 [1] as the one introducing this issue. It's
Brett's code, fixing a nasty crasher and adding a pre-built exception
(PyExc_RecursionErrorInst).

[1] http://svn.python.org/view?rev=58032&view=rev

P.S.: Thanks Thomas for correctly identifying an issue I mis-reported :)

[warsaw]

I'm not going to hold up the 2.6 alpha release for this, but will bump
it up for the first 2.6 beta.

[warsaw]

This is a bug that can be fixed after beta, so I'm knocking it back to
critical for beta 1.