Bug 29257

OK, I think I've traced the root of the differences in the behaviour:

XChat uses one embedded python interpreter per python script, and reloading/unloading a script causes that interpreter to be destroyed. DBus-python very clearly does something wrong in this case, and causes things to crash and deadlock.

Here's a simple test case (save as ~/.xchat2/crasher.py)

__module_name__ = "crasher" 
__module_version__ = "0.1" 
__module_description__ = "Crash or lockup xchat by using dbus bindings"
__module_author__ = "Maciej Katafiasz <email@mathrick.org>"

import dbus

bus = dbus.SessionBus()
bus.close() # This call is crucial

print "Crasher loaded"

# To lock xchat up, /py unload crasher. It will deadlock trying to end the embedded interpreter

The above will lock up the intepreter:


Program received signal SIGINT, Interrupt.
0x0012d422 in __kernel_vsyscall ()
(gdb) bt
#0  0x0012d422 in __kernel_vsyscall ()
#1  0x009e5245 in sem_wait@@GLIBC_2.1 () from /lib/tls/i686/cmov/libpthread.so.0
#2  0x0169ce10 in PyThread_acquire_lock (lock=0x8be71d8, waitflag=1) at ../Python/thread_pthread.h:349
#3  0x0166c798 in PyEval_RestoreThread (tstate=0x8ada348) at ../Python/ceval.c:353
#4  0x0168fa90 in PyGILState_Ensure () at ../Python/pystate.c:592
#5  0x0180073f in ?? () from /usr/lib/pymodules/python2.6/_dbus_bindings.so
#6  0x009c6124 in ?? () from /lib/libdbus-1.so.3
#7  0x009c6172 in ?? () from /lib/libdbus-1.so.3
#8  0x009aca93 in ?? () from /lib/libdbus-1.so.3
#9  0x017fd898 in ?? () from /usr/lib/pymodules/python2.6/_dbus_bindings.so
#10 0x0162b5bd in subtype_dealloc (self=<SessionBus at remote 0x93a0cec>) at ../Objects/typeobject.c:1019
#11 0x0160c779 in insertdict (mp=0x90c83e4, key='bus', hash=-455024823, value=None) at ../Objects/dictobject.c:459
#12 0x0160f1c4 in PyDict_SetItem (op=
    {'dbus': None, '__builtins__': <module at remote 0x8eadac4>, 'bus': None, '__package__': None, 'sys': <module at remote 0x8eaddc4>, '__module_name__': 'crasher', '__module_description__': 'Crash or lockup xchat by using dbus bindings', '__name__': '__main__', '__module_author__': 'Maciej Katafiasz <email@mathrick.org>', '__doc__': None, '__module_version__': '0.1'}, 
    key='bus', value=None) at ../Objects/dictobject.c:701
#13 0x0161146e in _PyModule_Clear (m=<module at remote 0x8eadcbc>) at ../Objects/moduleobject.c:138
#14 0x016845c9 in PyImport_Cleanup () at ../Python/import.c:441
#15 0x01691355 in Py_EndInterpreter (tstate=0x8b9a478) at ../Python/pythonrun.c:642
#16 0x015988c6 in ?? () from /usr/lib/xchat/plugins/python.so
#17 0x0159ad98 in ?? () from /usr/lib/xchat/plugins/python.so
#18 0x0159c1c1 in ?? () from /usr/lib/xchat/plugins/python.so
#19 0x080a0b0c in ?? ()
#20 0x0809eaa6 in ?? ()
#21 0x0809f7ec in ?? ()
#22 0x08071c36 in ?? ()
#23 0x00a0adcc in g_cclosure_marshal_VOID__VOID () from /usr/lib/libgobject-2.0.so.0
#24 0x009fd252 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#25 0x00a1199d in ?? () from /usr/lib/libgobject-2.0.so.0
#26 0x001b7a62 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#27 0x001b801f in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#28 0x001b82a2 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#29 0x001b83df in gtk_bindings_activate_event () from /usr/lib/libgtk-x11-2.0.so.0
#30 0x00203357 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#31 0x002802f4 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#32 0x009fb8b9 in ?? () from /usr/lib/libgobject-2.0.so.0
#33 0x009fd178 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#34 0x00a115e6 in ?? () from /usr/lib/libgobject-2.0.so.0
#35 0x00a12c33 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#36 0x00a13256 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#37 0x003ad306 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#38 0x003bf27f in gtk_window_propagate_key_event () from /usr/lib/libgtk-x11-2.0.so.0
#39 0x003c259c in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#40 0x002802f4 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#41 0x009fb8b9 in ?? () from /usr/lib/libgobject-2.0.so.0
#42 0x009fd252 in g_closure_invoke () from /usr/lib/libgobject-2.0.so.0
#43 0x00a115e6 in ?? () from /usr/lib/libgobject-2.0.so.0
#44 0x00a12c33 in g_signal_emit_valist () from /usr/lib/libgobject-2.0.so.0
#45 0x00a13256 in g_signal_emit () from /usr/lib/libgobject-2.0.so.0
#46 0x003ad306 in ?? () from /usr/lib/libgtk-x11-2.0.so.0
#47 0x00278a03 in gtk_propagate_event () from /usr/lib/libgtk-x11-2.0.so.0
#48 0x00279cd7 in gtk_main_do_event () from /usr/lib/libgtk-x11-2.0.so.0
#49 0x0056e35a in ?? () from /usr/lib/libgdk-x11-2.0.so.0
#50 0x00c135e5 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#51 0x00c172d8 in ?? () from /lib/libglib-2.0.so.0
#52 0x00c17817 in g_main_loop_run () from /lib/libglib-2.0.so.0
#53 0x0027a299 in gtk_main () from /usr/lib/libgtk-x11-2.0.so.0
#54 0x0806167b in ?? ()
#55 0x080ae7af in ?? ()
#56 0x00cb8bd6 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
#57 0x08055c71 in ?? ()

This is a different crash than the first one I reported, but it has a very small testcase. It does not lockup if bus.close() isn't called. Similarly, calling bus.close() in the original plugin I found crashes in jumped from being pretty random to completely reproducible as soon as I tried closing the bus in the (vain, obviously) hope of fixing the crashes.

(In reply to comment #0)
> The python bindings segfault in some situations when handling
> org.freedesktop.DBus.Error.NameHasNoOwner. This is due to the fact
> DBusPyException_ConsumeError:84 doesn't check exc before calling it with
> PyObject_SetAttrString, and sometimes exc can apparently be NULL.

I've added a check for that.

(In reply to comment #1)
> XChat uses one embedded python interpreter per python script, and
> reloading/unloading a script causes that interpreter to be destroyed.
> DBus-python very clearly does something wrong in this case

Bug #23831 caused something to be done wrong in finalizing/re-initializing an interpreter. Could you try again with dbus-python git master, or 0.83.2 when available, in which that bug is fixed?

In the absence of testing information I'm closing this as WORKSFORME. Please reopen, or open a new bug, if there are further problems.