Bug#1087173: xbrlapi blocks X11 session startup for ~135 seconds on Linux Mint 22.3 / LightDM / Cinnamon

[iohann_tyrell]

Hello,

I can reproduce this issue on Linux Mint 22.3 (Ubuntu 24.04 Noble base)
with LightDM and Cinnamon on X11.

The symptom was a black screen with a movable mouse cursor after entering
the password in LightDM. The Cinnamon desktop appeared only after
approximately 2-3 minutes.

The issue was reproducible with a newly-created user account, so it was
not caused by per-user Cinnamon configuration.

I also tested different kernels and graphics configurations. These did
not affect the delay.

I instrumented the LightDM session startup and found that the session was
blocked waiting for xbrlapi.

During the delay the process tree remained:

/bin/bash /usr/sbin/lightdm-session cinnamon-session-cinnamon
`- /bin/xbrlapi

For example, after 132 seconds:

USER PID PPID ELAPSED STAT WCHAN CMD
bobsyan 1407 1207 132 Ss do_wait /bin/bash /usr/sbin/lightdm-session cinnamon-session-cinnamon
bobsyan 1479 1407 132 S wait_woken /bin/xbrlapi

At approximately 134 seconds the same state was still present.

Immediately afterwards xbrlapi disappeared and PID 1407 exec'd:

/usr/lib/x86_64-linux-gnu/cinnamon-session-binary --session cinnamon

Cinnamon startup then continued.

Disabling the xbrlapi Xsession hook:

sudo mv /etc/X11/Xsession.d/90xbrlapi \
/etc/X11/Xsession.d/90xbrlapi.disabled

completely removed the long login delay.

Relevant BRLTTY packages on the system:

brltty 6.6-4ubuntu5
libbrlapi0.8 6.6-4ubuntu5

Another potentially important observation is the behaviour of TCP
connections to the BRLAPI port on loopback.

IPv4 fails immediately, as expected when nothing is listening:

127.0.0.1: ConnectionRefusedError: [Errno 111] Connection refused, 0.000 s

IPv6, however, does not return ECONNREFUSED and instead times out:

::1: TimeoutError: timed out, 5.004 s

IPv6 itself is enabled:

net.ipv6.conf.all.disable_ipv6 = 0
net.ipv6.conf.default.disable_ipv6 = 0
net.ipv6.conf.lo.disable_ipv6 = 0

There is no ipv6.disable kernel parameter:

BOOT_IMAGE=/boot/vmlinuz-7.0.0-31-generic
root=UUID=...
ro quiet splash

This suggests that xbrlapi may attempt the IPv6 loopback connection first
and remain blocked by the TCP connect timeout instead of failing quickly.

In this case, xbrlapi being started synchronously from the Xsession hook
causes the entire graphical desktop session to be delayed for roughly
two minutes.

Environment:

Distribution: Linux Mint 22.3 "Zena"
Ubuntu base: 24.04 Noble
Desktop: Cinnamon 6.6.9
Display manager: LightDM
Session type: X11
Kernel: 7.0.0-31-generic
BRLTTY: 6.6-4ubuntu5
libbrlapi0.8: 6.6-4ubuntu5

The issue was confirmed by monitoring the LightDM process tree once per
second. I have attached the complete monitoring log.

The workaround of disabling /etc/X11/Xsession.d/90xbrlapi has been
retested and the login delay disappears.

Please let me know if additional traces (strace of xbrlapi, nftables
rules, LightDM logs, etc.) would be useful.

Regards,Andre

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