jackdbus hanging - can't reproduce reliably

[jackaudio]

jackdbus hanging - can't reproduce reliably

[nedko]

If jack server is actually working but jackdbus doesn't respond via dbus interface, check whether the dbus loop in jackdbus is blocked for some reason. Also check for both jackd and jackdbus running.

[antgel]

@nedko Hi, thanks for responding. How can I check if the dbus loop is blocked? I am fairly technical but I know nothing about jack or dbus internals. jackd is never running, only jackdbus.

[nedko]

Start gdb and attach to the process. The D-Bus loop is in the main thread, in the main() function. If it is blocked forever in jack_controller_run() then something has gone wrong.

[antgel]

Hi, I forgot to ask which process to attach to. Anyway this is what I got when I attached gdb to the jackdbus process. Lower down, I'll paste what I got when I attached gdb to the jack_control process. Is it useful? If not, please tell me what I did wrong and I'll try again.

__lll_lock_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
135 ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S: No such file or directory.
(gdb) bt
#0 __lll_lock_wait ()
at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
#1 0x00007f836e3d7672 in _L_lock_953 ()
from /lib/x86_64-linux-gnu/libpthread.so.0
#2 0x00007f836e3d74da in __GI___pthread_mutex_lock (mutex=0x1b9f088)
at ../nptl/pthread_mutex_lock.c:114
#3 0x00007f836e658c8c in Jack::JackPosixMutex::Lock() ()
from /usr/lib/x86_64-linux-gnu/libjackserver.so.0
#4 0x00007f836e65b034 in ?? ()
from /usr/lib/x86_64-linux-gnu/libjackserver.so.0
#5 0x00007f836e65b07a in ?? ()
from /usr/lib/x86_64-linux-gnu/libjackserver.so.0
#6 0x00007f836e668349 in Jack::JackLockedEngine::ClientDeactivate(int) ()
from /usr/lib/x86_64-linux-gnu/libjackserver.so.0
#7 0x00007f836e669388 in ?? ()
from /usr/lib/x86_64-linux-gnu/libjackserver.so.0
#8 0x00007f836e638146 in Jack::JackClient::Deactivate() ()
from /usr/lib/x86_64-linux-gnu/libjackserver.so.0
#9 0x00007f836e634696 in jack_deactivate ()
from /usr/lib/x86_64-linux-gnu/libjackserver.so.0
#10 0x000000000040640d in ?? ()
#11 0x000000000040a4a4 in ?? ()
#12 0x000000000040479a in ?? ()
#13 0x00007f836db50326 in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#14 0x00007f836db42ca1 in dbus_connection_dispatch ()
from /lib/x86_64-linux-gnu/libdbus-1.so.3
#15 0x00007f836db42f32 in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#16 0x0000000000405b6e in ?? ()
#17 0x00007f836d260ec5 in __libc_start_main (main=0x4058ae, argc=2,
argv=0x7fff49adaf58, init=, fini=,
rtld_fini=, stack_end=0x7fff49adaf48) at libc-start.c:287
#18 0x00000000004043d9 in ?? ()

jack_control:
Attaching to program: /usr/bin/python, process 11028
Reading symbols from /lib/x86_64-linux-gnu/libpthread.so.0...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libpthread-2.19.so...done.
done.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Loaded symbols for /lib/x86_64-linux-gnu/libpthread.so.0
Reading symbols from /lib/x86_64-linux-gnu/libdl.so.2...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libdl-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/libdl.so.2
Reading symbols from /lib/x86_64-linux-gnu/libutil.so.1...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libutil-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/libutil.so.1
Reading symbols from /lib/x86_64-linux-gnu/libz.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib/x86_64-linux-gnu/libz.so.1
Reading symbols from /lib/x86_64-linux-gnu/libm.so.6...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libm-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/libm.so.6
Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/ld-2.19.so...done.
done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /usr/lib/python2.7/dist-packages/_dbus_bindings.so...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/python2.7/dist-packages/_dbus_bindings.so
Reading symbols from /lib/x86_64-linux-gnu/libdbus-1.so.3...(no debugging symbols found)...done.
Loaded symbols for /lib/x86_64-linux-gnu/libdbus-1.so.3
Reading symbols from /usr/lib/python2.7/lib-dynload/pyexpat.x86_64-linux-gnu.so...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/python2.7/lib-dynload/pyexpat.x86_64-linux-gnu.so
Reading symbols from /lib/x86_64-linux-gnu/libexpat.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib/x86_64-linux-gnu/libexpat.so.1
0x00007f716e66f020 in __poll_nocancel ()
at ../sysdeps/unix/syscall-template.S:81
81 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) bt
#0 0x00007f716e66f020 in __poll_nocancel ()
at ../sysdeps/unix/syscall-template.S:81
#1 0x00007f716df2c5f8 in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#2 0x00007f716df2b59f in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#3 0x00007f716df15c4c in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#4 0x00007f716df165f9 in ?? () from /lib/x86_64-linux-gnu/libdbus-1.so.3
#5 0x00007f716e15ff9a in ?? ()
from /usr/lib/python2.7/dist-packages/_dbus_bindings.so
#6 0x000000000052bb50 in PyEval_EvalFrameEx ()
#7 0x000000000052b66a in PyEval_EvalFrameEx ()
#8 0x000000000056a89a in ?? ()
#9 0x00000000004d0234 in ?? ()
#10 0x00000000005062d6 in PyObject_Call ()
#11 0x000000000059d11c in ?? ()
#12 0x000000000052b355 in PyEval_EvalFrameEx ()
#13 0x000000000052b66a in PyEval_EvalFrameEx ()
#14 0x000000000054d6c4 in PyEval_EvalCodeEx ()
#15 0x00000000005aca72 in PyEval_EvalCode ()
#16 0x00000000005b839b in ?? ()
#17 0x00000000004694b6 in PyRun_FileExFlags ()
#18 0x00000000004699ef in PyRun_SimpleFileExFlags ()
#19 0x000000000046af64 in Py_Main ()
#20 0x00007f716e5a2ec5 in __libc_start_main (main=0x46b022

, argc=3,
argv=0x7fff2ca4c4c8, init=, fini=,
rtld_fini=, stack_end=0x7fff2ca4c4b8) at libc-start.c:287
#21 0x000000000057a4ee in _start ()
(gdb)

[nedko]

I was talking about jackdbus. Obviously something went wrong with libjackserver.so (jack server), jack_deactivate () deadlocked. If you want to find the exact reason for the deadlock, you will probably need backtraces from other jack server threads and/or verbose logs enabled.

[antgel]

I found the answer in the end. It seems that when a2jmidid is running, and jack is stopped (at least jackdbus, not sure about regular jack), that a2jmidid shuts down, leaving things in some kind of weird state. When the user restarts jack and then tries to restart a2jmidid, a2jmidid refuses to start. I'll try to raise a bug against a2jmidid, but I'll close this, as I don't think it's a jack issue.