Bug 1457769

*** This bug has been marked as a duplicate of bug 1450075 ***

I think there is a race.


We initialize GDBus Object Manager asyncronously. Note that this means, running sync on another thread:

static void
async_initable_iface_init (GAsyncInitableIface *async_initable_iface)
{
  /* for now, just use default: run GInitable code in thread */
}



Then, thread 2 is in process of g_initable_init(), while thread 1 receives InterfacesRemoved signal.

GDBus code is certainly broken here, because on thread 2 the initialization is like:

   - get-all-objects-sync
   - for all-objects:
        add_interface()
            take mutex & add interface

while on thread 1 it races with add_interface.


You never know whether a signal on thread 1 happened before get-all-objects-sync (and should be ignored), or after (and should be considered).

I think patch https://bugzilla.gnome.org/show_bug.cgi?id=783795 is wrong. You *must* process all signals during process_get_all_result(). But *if* you handle any (asynchrnous) signals, you *must* ignore whether the object is present in the requested synchronous get-all.

Meaning:

  if you get an InterfaceRemoved signal, you must ignore the same signal if it is present in the synchronous get-all. 





(gdb) thread 2
[Switching to thread 2 (Thread 0x3fff7f7ef010 (LWP 29564))]
#0  .syscall () at ../sysdeps/unix/sysv/linux/powerpc/syscall.S:29
29              PSEUDO_RET
(gdb) bt
#0  0x00003fff8716b8b4 in .syscall () at ../sysdeps/unix/sysv/linux/powerpc/syscall.S:29
#1  0x00003fff872f6054 in g_mutex_lock_slowpath (mutex=<optimized out>) at gthread-posix.c:1313
#2  0x00003fff87658ca0 in add_interfaces (manager=manager@entry=0x1002b1234c0 [GDBusObjectManagerClient], object_path=0x3fff7400ac20 "/org/freedesktop/NetworkManager/Settings/6", ifaces_and_properties=0x3fff7401aea0, name_owner=name_owner@entry=0x3fff70041170 ":1.10600") at gdbusobjectmanagerclient.c:1440
#3  0x00003fff87659e54 in process_get_all_result (manager=0x1002b1234c0 [GDBusObjectManagerClient], value=<optimized out>, name_owner=0x3fff70041170 ":1.10600")
    at gdbusobjectmanagerclient.c:1647
#4  0x00003fff8765a7e4 in initable_init (initable=0x1002b1234c0, cancellable=0x0, error=0x3fff7f7ee3d0) at gdbusobjectmanagerclient.c:1400
#5  0x00003fff8759c328 in g_initable_init (initable=0x1002b1234c0, cancellable=0x0, error=0x3fff7f7ee3d0) at ginitable.c:112
#6  0x00003fff87558774 in async_init_thread (task=0x1002b12f040 [GTask], source_object=<optimized out>, task_data=<optimized out>, cancellable=<optimized out>) at gasyncinitable.c:257
#7  0x00003fff875e1294 in g_task_thread_pool_thread (thread_data=0x1002b12f040, pool_data=<optimized out>) at gtask.c:1304
#8  0x00003fff87373e90 in g_thread_pool_thread_proxy (data=<optimized out>) at gthreadpool.c:307
#9  0x00003fff87372ba4 in g_thread_proxy (data=0x1002b1110a0) at gthread.c:784
#10 0x00003fff8789c95c in start_thread (arg=0x3fff7f7ef010) at pthread_create.c:310
#11 0x00003fff87173bbc in .__clone () at ../sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S:109
(gdb) thread 1
[Switching to thread 1 (Thread 0x3fff86a151b0 (LWP 29562))]
#0  .__strcmp_power8 () at ../sysdeps/powerpc/powerpc64/power8/strcmp.S:49
49              ld      r8,0(r3)
(gdb) bt
#0  0x00003fff8710095c in .__strcmp_power8 () at ../sysdeps/powerpc/powerpc64/power8/strcmp.S:49
#1  0x00003fff87322f00 in g_str_equal (v1=<optimized out>, v2=<optimized out>) at ghash.c:1846
#2  0x00003fff87321c30 in g_hash_table_lookup (hash_return=<synthetic pointer>, key=0x1002b12ef40, hash_table=0x1002b0f7180 = {...}) at ghash.c:396
#3  0x00003fff87321c30 in g_hash_table_lookup (hash_table=0x1002b0f7180 = {...}, key=0x1002b12ef40) at ghash.c:1147
#4  0x00003fff87659b40 in on_control_proxy_g_signal (interface_names=0x1002b1003d0, object_path=0x1002b12ef40 "/org/freedesktop/NetworkManager/ActiveConnection/25", manager=0x1002b1234c0 [GDBusObjectManagerClient]) at gdbusobjectmanagerclient.c:1580
#5  0x00003fff87659b40 in on_control_proxy_g_signal (proxy=<optimized out>, sender_name=<optimized out>, signal_name=<optimized out>, parameters=0x3fff74092f60, user_data=0x1002b1234c0)
    at gdbusobjectmanagerclient.c:1682
#6  0x00003fff86c580dc in .ffi_call_LINUX64 () at ../src/powerpc/linux64.S:116
#7  0x00003fff86c57808 in ffi_call (cif=<optimized out>, fn=<optimized out>, rvalue=0x3fffc13fd650, avalue=<optimized out>) at ../src/powerpc/ffi.c:985
#12 0x00003fff87491e18 in <emit signal ??? on instance 0x3fff7000cd10 [GDBusProxy]> (instance=<optimized out>, signal_id=<optimized out>, detail=<optimized out>) at gsignal.c:3447
    #8  0x00003fff8746e5cc in g_cclosure_marshal_generic (closure=0x3fff70040df0, return_gvalue=0x0, n_param_values=<optimized out>, param_values=<optimized out>, invocation_hint=<optimized out>, marshal_data=0x0) at gclosure.c:1490
    #9  0x00003fff8746d8c8 in g_closure_invoke (closure=0x3fff70040df0, return_value=0x0, n_param_values=<optimized out>, param_values=0x3fffc13fda40, invocation_hint=0x3fffc13fd920)
    at gclosure.c:804
    #10 0x00003fff874886b8 in signal_emit_unlocked_R (node=node@entry=0x3fff7003c720, detail=detail@entry=0, instance=instance@entry=0x3fff7000cd10, emission_return=emission_return@entry=0x0, instance_and_params=instance_and_params@entry=0x3fffc13fda40) at gsignal.c:3635
    #11 0x00003fff87491b80 in g_signal_emit_valist (instance=0x3fff7000cd10, signal_id=<optimized out>, detail=<optimized out>, var_args=<optimized out>) at gsignal.c:3391
#13 0x00003fff87641ef4 in on_signal_received (connection=<optimized out>, sender_name=0x3fff740933f0 ":1.10600", object_path=<optimized out>, interface_name=<optimized out>, signal_name=0x3fff7408f250 "InterfacesRemoved", parameters=0x3fff74092f60, user_data=<optimized out>) at gdbusproxy.c:917
#14 0x00003fff87629948 in emit_signal_instance_in_idle_cb (data=0x3fff7408eca0) at gdbusconnection.c:3705
#15 0x00003fff87336694 in g_idle_dispatch (source=0x3fff7408f140, callback=<optimized out>, user_data=<optimized out>) at gmain.c:5543
#16 0x00003fff8733bc28 in g_main_context_dispatch (context=0x1002b110e90) at gmain.c:3201
#17 0x00003fff8733bc28 in g_main_context_dispatch (context=0x1002b110e90) at gmain.c:3854
#18 0x00003fff8733c0b8 in g_main_context_iterate (context=0x1002b110e90, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at gmain.c:3927
#19 0x00003fff8733c5d0 in g_main_loop_run (loop=0x1002b1052c0) at gmain.c:4123
#20 0x0000000095985a24 in main (argc=<optimized out>, argv=<optimized out>) at clients/cli/nmcli.c:614



What I still don't understand, is how the crash could happen... :(


I think, for now we should workaround this, by initializing the object manager synchrnously.