systemd 240 bug?

[RoEdAl]

Fresh install on RPi3 (armv7) with additional packages: lightdm, lightdm-gtk-greeter, xorg-server, and xf86-video-fbturbo-git. No additional configuration.

Now I run command:
$this->bbcode_second_pass_code('', 'systemctl start lightdm')
and lightdm-gtk-greeter process hangs with 100% CPU usage on one core (no logon screen). Stopping this lightdm service takes about minute:
$this->bbcode_second_pass_code('', '
● lightdm.service - Light Display Manager
Loaded: loaded (/usr/lib/systemd/system/lightdm.service; disabled; vendor preset: disabled)
Active: failed (Result: timeout) since Sat 2019-01-26 12:55:44 CET; 1min 2s ago
Docs: man:lightdm(1)
Process: 325 ExecStart=/usr/bin/lightdm (code=killed, signal=KILL)
Main PID: 325 (code=killed, signal=KILL)

Jan 26 12:50:22 FbAlARM systemd[1]: Starting Light Display Manager...
Jan 26 12:50:22 FbAlARM systemd[1]: Started Light Display Manager.
Jan 26 12:50:26 FbAlARM lightdm[362]: pam_unix(lightdm-greeter:session): session opened for user lightdm by (uid=0)
Jan 26 12:54:13 FbAlARM systemd[1]: Stopping Light Display Manager...
Jan 26 12:55:44 FbAlARM systemd[1]: lightdm.service: State 'stop-sigterm' timed out. Killing.
Jan 26 12:55:44 FbAlARM systemd[1]: lightdm.service: Killing process 325 (lightdm) with signal SIGKILL.
Jan 26 12:55:44 FbAlARM systemd[1]: lightdm.service: Main process exited, code=killed, status=9/KILL
Jan 26 12:55:44 FbAlARM systemd[1]: lightdm.service: Failed with result 'timeout'.
Jan 26 12:55:44 FbAlARM systemd[1]: Stopped Light Display Manager.')
Contents of /var/log/lightdm/seat0-greeter.log:
$this->bbcode_second_pass_code('', '** Message: 12:50:28.741: Starting lightdm-gtk-greeter 2.0.6 (Sep 30 2018, 13:00:48)

(process:375): GLib-ERROR **: 12:50:28.863: creating thread 'gmain': Error creating thread: Resource temporarily unavailable')
The same on RPi Zero, oLinuXino Lime A10/A20 and (officialy unsupported, I know) Orange Pi One.
Downgrading systemd to version 239 helps.

But on RPi3 with mainline kernel (aarch64) lightdm-gtk-greeter works fine (logon window is displayed).
Contents of /var/log/lightdm/seat0-greeter.log:

$this->bbcode_second_pass_code('', '** Message: 12:38:05.330: Starting lightdm-gtk-greeter 2.0.6 (Sep 30 2018, 13:00:48)
** Message: 12:38:05.349: [Configuration] Reading file: /etc/lightdm/lightdm-gtk-greeter.conf

** (lightdm-gtk-greeter:386): WARNING **: 12:38:06.838: [PIDs] Failed to execute command: /usr/lib/at-spi2-core/at-spi-bus-launcher

** (lightdm-gtk-greeter:386): WARNING **: 12:38:06.850: [PIDs] Failed to execute command: upstart')
It also works fine on Orange Pi PC2 (also aarch64). Is this a systemd 240 bug?

[RoEdAl]

I found quick fix at: lightdm does mlockall() which is not compatible with systemd-240.

Just add $this->bbcode_second_pass_code('', 'LimitMEMLOCK=4G') to lightdm.service.

See also: mlockall() call needs to be removed. So it seems this is a bug in lightDM.