[mod_python] Re: python exceptions cause Apache to crash

Graham Dumpleton graham.dumpleton at gmail.com
Wed Aug 6 19:27:13 EDT 2008


2008/8/7 Jason Carver <ynj0qeh02 at sneakemail.com>:
> Great, thanks for your help!  Is there a good place for me to file a feature
> request to have mod_python do something besides crash in this case?

The problem has been discussed before, but can't see that there is an
issue for it. Issues can be created at:

  http://issues.apache.org/jira/browse/MODPYTHON-202

Yes Python could protect against this so a crash doesn't occur, but
your code shouldn't have been doing that in the first place.

Graham

> For reference, I have code here to demonstrate the bug and workaround:
>
> def testCrash(req):
>     """
>     Reliably crash server (on 2nd page access)
>     Open as: http://server/index.py/testCrash
>     """
>     handler = logging.StreamHandler(req)
>     logging.getLogger('').addHandler( handler )
>     logging.exception('I crash')
>
>     #removing this line will cause an apache crash on the
>     #    second web page access
>     logging.getLogger('').removeHandler(handler)
>
> I have confirmed that the workaround works reliably for me.
>
> Cheers,
> Jason
>
> On Tue, Aug 5, 2008 at 8:36 PM, Graham Dumpleton
> graham.dumpleton-at-gmail.com |public mailing list|
> <a9ghk53mp50t at sneakemail.com> wrote:
>>
>> Just realised what the problem is, rather obvious really.
>>
>> You are supplying a mod_python request object 'req' to:
>>
>>  logging.getLogger('').addHandler(logging.StreamHandler(req))
>>
>> You can't do that, as the logging handler you are creating will
>> persist beyond the lifetime of the internals of the 'req' object.
>> Thus, when logging tries to access it later, it will crash Apache.
>>
>> In other words, 'req' is just a wrapper for some internal Apache data
>> structures which will go away. The mod_python code doesn't currently
>> try and protect itself from user code making the mistake of retaining
>> the 'req' object longer than it should and then accessing those
>> internals.
>>
>> Graham
>>
>> 2008/8/6 Jason Carver <ynj0qeh02 at sneakemail.com>:
>> > If I try to install mod_python without python 2.5 installed, mod_python
>> > refuses, so I assume you mean uninstall all versions of python, then
>> > install
>> > python 2.5.2, then mod_python-3.3.1.win32-py2.5-Apache2.2.exe
>> >
>> > I did that, with no changes.  I get the same Traceback during mod_python
>> > install and I can still reproduce the crash reliably.
>> >
>> > Bug requirements update: It does not matter if I test the req object, it
>> > only matters if the req object has something set.  So these are the new
>> > requirements to reproduce the bug
>> >
>> > use built in logging module
>> > raise Exception
>> > call page with variables (ie~ http://localhost/index.py?action=boom)
>> > use the following code:
>> >
>> > import logging
>> >
>> > def index(req):
>> >     """Handles all Browser Requests"""
>> >     try:
>> >         logging.getLogger('').addHandler( logging.StreamHandler(req) )
>> >
>> >         raise Exception('Goodbye Apache')
>> >
>> >     except Exception, e:
>> >         logging.exception('I crash')
>> >         raise
>> >
>> > So there seems to be some kind of three way interaction between the
>> > logging
>> > module, the apache req module, and exception handling.  If any one of
>> > the
>> > three are not involved, apache does not crash...
>> >
>> > For now I can use a home-grown logger to get around the bug, but I hate
>> > to
>> > build code that already exists and make future developers have to learn
>> > my
>> > logger instead of the built-in one.
>> >
>> > Cheers,
>> > Jason
>> >
>> > On Mon, Aug 4, 2008 at 9:44 PM, Graham Dumpleton
>> > graham.dumpleton-at-gmail.com |public mailing list|
>> > <a9ghk53mp50t at sneakemail.com> wrote:
>> >>
>> >> Please use reply-all and keep discussion on the list, don't reply just
>> >> to
>> >> me.
>> >>
>> >> Have you tried uninstalling all versions of Python and mod_python
>> >> first and then install it? Ie., don't install when you have existing
>> >> versions on the system.
>> >>
>> >> When installing packages, are you doing it as a user with
>> >> administrator privileges?
>> >>
>> >> Graham
>> >>
>> >> 2008/8/5  <ynj0qeh02 at sneakemail.com>:
>> >> > Unfortunately, when I tried to install the mod_python 3.3.1 for 2.5 I
>> >> > got
>> >> > this traceback:
>> >> > Traceback (most recent call last):
>> >> >   File "boot_com_servers.py", line 21, in <module>
>> >> >   File "C:\Python25\Lib\site-packages\pythoncom.py", line 3, in
>> >> > <module>
>> >> >     pywintypes.__import_pywin32_system_module__("pythoncom",
>> >> > globals())
>> >> >   File "C:\Python25\Lib\site-packages\win32\Lib\pywintypes.py", line
>> >> > 98,
>> >> > in
>> >> > __import_pywin32_system_module__
>> >> >     ('.dll', 'rb', imp.C_EXTENSION))
>> >> > ImportError: DLL load failed: The specified procedure could not be
>> >> > found.
>> >> >
>> >> > and when I try to start apache 2 anyway, it says "The requested
>> >> > operation
>> >> > has failed!"
>> >> >
>> >> > That's why I was using the version for 2.4.
>> >> >
>> >> > On Mon, Aug 4, 2008 at 9:21 PM, Graham Dumpleton
>> >> > graham.dumpleton-at-......... |public mailing list| <...> wrote:
>> >> >>
>> >> >> 2008/8/5  <ynj0qeh02 at sneakemail.com>:
>> >> >> > Thanks for the quick reply!  Answers inline...
>> >> >> >
>> >> >> > On Mon, Aug 4, 2008 at 7:28 PM, Graham Dumpleton
>> >> >> > graham.dumpleton-at-......... |public mailing list| <...> wrote:
>> >> >> >>
>> >> >> >> What operating system? What version of Python? What version of
>> >> >> >> mod_python?
>> >> >> >
>> >> >> > I am on Windows XP SP3 using Python 2.5 in mod_python 3.3.1
>> >> >> >
>> >> >> > I hacked the binary to use 2.5 on Windows, but the same problem is
>> >> >> > reproducible on Ubuntu 7.10 using the latest source from svn
>> >> >> > compiled
>> >> >> > with
>> >> >> > python 2.5.
>> >> >> >
>> >> >> >> What startup messages for mod_python are in the Apache error log?
>> >> >> >
>> >> >> >
>> >> >> > [Mon Aug 04 20:03:21 2008] [notice] Server built: Nov  7 2007
>> >> >> > 11:48:48
>> >> >> > [Mon Aug 04 20:03:21 2008] [notice] Parent: Created child process
>> >> >> > 27164
>> >> >> > [Mon Aug 04 20:03:22 2008] [error] python_init: Python version
>> >> >> > mismatch,
>> >> >> > expected '2.4.3', found '2.5'.
>> >> >>
>> >> >> This is why it is probably breaking. Install mod_python compiled
>> >> >> against Python 2.5. The version you are using was compiled against
>> >> >> older version of Python.
>> >> >>
>> >> >> Fix your installation and try again.
>> >> >>
>> >> >> Do you get similar warnings on your other platform as well?
>> >> >>
>> >> >> Graham
>> >> >>
>> >> >> > [Mon Aug 04 20:03:22 2008] [error] python_init: Python executable
>> >> >> > found
>> >> >> > 'C:\\xampp\\apache\\bin\\apache.exe'.
>> >> >> > [Mon Aug 04 20:03:22 2008] [error] python_init: Python path being
>> >> >> > used
>> >> >> > 'C:\\Program
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> > Files\\OpenLibraries\\python;C:\\WINDOWS\\system32\\python25.zip;C:\\Python25\\Lib;C:\\Python25\\DLLs;C:\\Python25\\Lib\\lib-tk;;C:\\xampp\\apache\\bin'.
>> >> >> > [Mon Aug 04 20:03:22 2008] [notice] mod_python: Creating 8 session
>> >> >> > mutexes
>> >> >> > based on 0 max processes and 250 max threads.
>> >> >> >
>> >> >> >>
>> >> >> >>
>> >> >> >> What is the mod_python configuration you have in Apache
>> >> >> >> configuration
>> >> >> >> files?
>> >> >> >
>> >> >> >
>> >> >> > PythonOption mod_python.mutex_directory "/pytmp"
>> >> >> > PythonOption mod_python.mutex_locks 8
>> >> >> >
>> >> >> > AliasMatch      ^/slique(.*)        'C:/Documents and
>> >> >> > Settings/Jason/My
>> >> >> > Documents/Coding/eclipse-workspace/slique-dev/src/$1'
>> >> >> >
>> >> >> > <Directory 'C:/Documents and Settings/Jason/My
>> >> >> > Documents/Coding/eclipse-workspace/slique-dev/src'>
>> >> >> >     Options Indexes ExecCGI FollowSymLinks MultiViews
>> >> >> >     AllowOverride All
>> >> >> >
>> >> >> >     AddHandler mod_python .py
>> >> >> >     PythonHandler mod_python.publisher
>> >> >> >     PythonDebug On
>> >> >> >     PythonPath "sys.path + ['C:/Documents and Settings/Jason/My
>> >> >> > Documents/Coding/eclipse-workspace/slique-dev/src']"
>> >> >> >
>> >> >> > </Directory>
>> >> >> >
>> >> >> >>
>> >> >> >>
>> >> >> >> Specifically, are you setting PythonPath directive in really
>> >> >> >> strange
>> >> >> >> ways?
>> >> >> >
>> >> >> > PythonPath is set this way
>> >> >> > PythonPath "sys.path + ['C:/Documents and Settings/Jason/My
>> >> >> > Documents/Coding/eclipse-workspace/slique-dev/src']"
>> >> >> >
>> >> >> >>
>> >> >> >>
>> >> >> >> Does it happen if you don't use the 'logging' module?
>> >> >> >
>> >> >> > If I comment out logging.exception('I crash'), then the traceback
>> >> >> > prints
>> >> >> > to
>> >> >> > screen as expected.
>> >> >> >
>> >> >> >>
>> >> >> >> Graham
>> >> >> >>
>> >> >> >> 2008/8/5 Jason Carver <ynj0qeh02 at sneakemail.com>:
>> >> >> >> > Here is code that consistently crashes Apache for me:
>> >> >> >> >
>> >> >> >> > import logging
>> >> >> >> >
>> >> >> >> > def index(req):
>> >> >> >> >     """Handles all Browser Requests"""
>> >> >> >> >     try:
>> >> >> >> >         reqHandler = logging.StreamHandler(req)
>> >> >> >> >         logging.getLogger('').addHandler(reqHandler)
>> >> >> >> >         if req.form.has_key('action'):
>> >> >> >> >             raise Exception('Goodbye Apache')
>> >> >> >> >     except Exception, e:
>> >> >> >> >         logging.exception('I crash')
>> >> >> >> >         raise
>> >> >> >> >
>> >> >> >> > Now just go to the site with /?action=dosomething and it will
>> >> >> >> > crash
>> >> >> >> >
>> >> >> >> > Removing the if statement, the exception, or the logger are all
>> >> >> >> > ways
>> >> >> >> > of
>> >> >> >> > alleviating the crash, but none of them should be necessary.
>> >> >> >> >
>> >> >> >> > Cheers,
>> >> >> >> > Jason
>> >> >> >> >
>> >> >> >> > On Mon, Aug 4, 2008 at 2:51 PM, Jason Carver
>> >> >> >> > <ynj0qeh02 at sneakemail.com>
>> >> >> >> > wrote:
>> >> >> >> >>
>> >> >> >> >> Hi all,
>> >> >> >> >>
>> >> >> >> >> I am having the craziest error, confirmed on both a LAMPython
>> >> >> >> >> and
>> >> >> >> >> WAMPython setup: exceptions in mod_python are causing Apache
>> >> >> >> >> to
>> >> >> >> >> crash
>> >> >> >> >> hard.
>> >> >> >> >> Even stranger is that the exceptions have to meet a few
>> >> >> >> >> specific
>> >> >> >> >> conditions
>> >> >> >> >> to cause Apache to crash.
>> >> >> >> >>
>> >> >> >> >> As best I can tell those conditions include:
>> >> >> >> >>
>> >> >> >> >> raising an exception (this problem always goes away if the
>> >> >> >> >> exception
>> >> >> >> >> is
>> >> >> >> >> commented out)
>> >> >> >> >> having the exception be inside an if-block that tests a
>> >> >> >> >> dictionary
>> >> >> >> >> (the
>> >> >> >> >> problem goes away if I do something like """if 'hello' ==
>> >> >> >> >> 'hello':
>> >> >> >> >> raise
>> >> >> >> >> Exception('goodbye')""")
>> >> >> >> >> catching the exception and logging it using the python
>> >> >> >> >> built-in
>> >> >> >> >> logging.exception(e) (the problem goes away if I comment out
>> >> >> >> >> the
>> >> >> >> >> logger)
>> >> >> >> >>
>> >> >> >> >> Apache does not write anything to its error.log, so it was a
>> >> >> >> >> bit
>> >> >> >> >> of
>> >> >> >> >> an
>> >> >> >> >> adventure to discover all these elements.
>> >> >> >> >>
>> >> >> >> >> Any ideas?
>> >> >> >> >>
>> >> >> >> >> Cheers,
>> >> >> >> >> Jason
>> >> >> >> >
>> >> >> >> > _______________________________________________
>> >> >> >> > Mod_python mailing list
>> >> >> >> > Mod_python at modpython.org
>> >> >> >> > http://mailman.modpython.org/mailman/listinfo/mod_python
>> >> >> >> >
>> >> >> >> >
>> >> >> >
>> >> >> >
>> >> >
>> >> >
>> >
>> >
>> > _______________________________________________
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>> > Mod_python at modpython.org
>> > http://mailman.modpython.org/mailman/listinfo/mod_python
>> >
>> >
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