Bug#853132: pulseaudio-module-jack: modules fail to load due to real-time scheduling

[Vít Novotný]

Package: pulseaudio-module-jack
Version: 9.0-5
Severity: grave
Justification: renders package unusable

Dear Maintainer,

After installing pulseaudio-module-jack, running jackd via

    $ jackd -d alsa

and executing

    $ pactl load-module module-jack-sink
    $ pactl load-module module-jack-source

the following messages are written out to `/var/log/syslog`:

    Jan 30 01:19:36 inspiron pulseaudio[1198]: [pulseaudio] sink.c: Default and alternate sample rates are the same.
    Jan 30 01:19:36 inspiron pulseaudio[1198]: [pulseaudio] module-jack-sink.c: JACK error >Cannot use real-time scheduling (RR/5)(1: Operation not permitted)<
    Jan 30 01:19:36 inspiron pulseaudio[1198]: [pulseaudio] module-jack-sink.c: JACK error >JackClient::AcquireSelfRealTime error<
    Jan 30 01:19:48 inspiron pulseaudio[1198]: [pulseaudio] source.c: Default and alternate sample rates are the same.
    Jan 30 01:19:48 inspiron pulseaudio[1198]: [pulseaudio] module-jack-source.c: JACK error >Cannot use real-time scheduling (RR/5)(1: Operation not permitted)<
    Jan 30 01:19:48 inspiron pulseaudio[1198]: [pulseaudio] module-jack-source.c: JACK error >JackClient::AcquireSelfRealTime error<

Note that the debian installer correctly produced the file
`/etc/security/limits.d/audio.conf` with the following contents:

    # Provided by the jackd package.
    #
    # Changes to this file will be preserved.
    #
    # If you want to enable/disable realtime permissions, run
    #
    #    dpkg-reconfigure -p high jackd

    @audio   -  rtprio     95
    @audio   -  memlock    unlimited
    #@audio   -  nice      -19

and both my user account and pulse are in the unix group `audio`.  Since
`jackd` (package `jackd2`, 1.9.10+20150825git1ed50c92~dfsg-4) alone has
no issue setting its real-time priority to 20 and above, this seems to
be an issue with `libjack`.

If I run

    $ pactl set-default-sink jack_out
    $ pactl set-default-source jack_in

afterwards, the pulseaudio default sink and source are redirected, but
no sound results (userland applications such as mpv claim that the
,,stream is suspended``). If I run `jackd` outside real-time mode:

    $ jackd --no-realtime -d alsa

then only the following logs are produced:

    Jan 30 01:19:36 inspiron pulseaudio[1198]: [pulseaudio] sink.c: Default and alternate sample rates are the same.
    Jan 30 01:19:48 inspiron pulseaudio[1198]: [pulseaudio] source.c: Default and alternate sample rates are the same.

but after running

    $ pactl set-default-sink jack_out
    $ pactl set-default-source jack_in

there is no sound nevertheless.

Note that both pulseaudio and jack work flawlessly separately. The
issue is in making pulseaudio work as a jack client.

-- System Information:
Debian Release: 9.0
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.9.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=cs_CZ.UTF-8, LC_CTYPE=cs_CZ.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages pulseaudio-module-jack depends on:
ii  libc6                             2.24-8
ii  libcap2                           1:2.25-1
ii  libdbus-1-3                       1.10.14-1
ii  libjack-jackd2-0 [libjack-0.116]  1.9.10+20150825git1ed50c92~dfsg-4+b1
ii  libpulse0                         9.0-5
ii  pulseaudio                        9.0-5

pulseaudio-module-jack recommends no packages.

pulseaudio-module-jack suggests no packages.

-- no debconf information