Black screen, 100 percent CPU usage

Bug #1635125 reported by Dominik Schrempf on 2016-10-20
12
This bug affects 2 people
Affects Status Importance Assigned to Milestone
LightDM GTK+ Greeter
New
Unknown

Bug Description

Hello,

after boot and lock screen (`lightdm-locker-command -l`) the screen stays black and lightdm uses 100 percent CPU. When I click on the black screen, the greeter appears with wrong resolution but sometimes (I did not find out when exactly) it flickers and changes to the correct one.

This happens on my laptop with closed lid in a docking station with two external monitors.

Name : lightdm
Version : 1:1.18.3-1
Name : lightdm-gtk-greeter
Version : 1:2.0.2-1

`uname -a`
Linux schwarzbaer 4.8.2-1-ARCH #1 SMP PREEMPT Mon Oct 17 08:11:46 CEST 2016 x86_64 GNU/Linux

During the high CPU usage, I get:
`ps ax | grep lightdm`
  578 ? SLsl 0:00 /usr/bin/lightdm
  591 tty7 Ssl+ 0:34 /usr/lib/xorg-server/Xorg :0 -seat seat0 -auth /run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
 1596 ? Sl 0:00 lightdm --session-child 12 19
 4264 tty8 Ssl+ 0:00 /usr/lib/xorg-server/Xorg :1 -seat seat0 -auth /run/lightdm/root/:1 -nolisten tcp vt8 -novtswitch
 4270 ? Sl 0:00 lightdm --session-child 19 23
 4280 ? Ssl 0:03 /usr/sbin/lightdm-gtk-greeter
 4307 ? S 0:00 lightdm --session-child 13 23
 4328 tty2 S+ 0:00 grep lightdm

So maybe there are two sessions started somehow?

`sudo tail -n 30 /var/log/lightdm/lightdm.log`
[+1819.28s] DEBUG: Seat seat0 changes active session to c6
[+1852.17s] DEBUG: Seat seat0 changes active session to c7
[+1852.17s] DEBUG: Session c7 is already active
[+1857.07s] DEBUG: Continue authentication
[+1857.08s] DEBUG: Session pid=4307: Authentication complete with return value 0: Success
[+1857.08s] DEBUG: Authenticate result for user dominik: Success
[+1857.08s] DEBUG: User dominik authorized
[+1857.08s] DEBUG: Greeter sets language en_US.utf8
[+1857.14s] DEBUG: Greeter requests session xmonad-dominik
[+1857.14s] DEBUG: Seat seat0: Returning to existing user session dominik
[+1857.14s] DEBUG: Unlocking login1 session c2
[+1857.15s] DEBUG: Activating VT 7
[+1857.15s] WARNING: Error using VT_WAITACTIVE 7 on /dev/tty0: Interrupted system call
[+1857.15s] DEBUG: Seat seat0: Stopping greeter
[+1857.15s] DEBUG: Session pid=4270: Sending SIGTERM
[+1857.15s] DEBUG: Activating login1 session c2
[+1857.15s] DEBUG: Session pid=4307: Exited with return value 0
[+1857.15s] DEBUG: Seat seat0: Session stopped
[+1857.18s] DEBUG: Greeter closed communication channel
[+1857.18s] DEBUG: Session pid=4270: Exited with return value 0
[+1857.18s] DEBUG: Seat seat0: Session stopped
[+1857.18s] DEBUG: Seat seat0: Stopping display server, no sessions require it
[+1857.18s] DEBUG: Sending signal 15 to process 4264
[+1857.50s] DEBUG: Seat seat0 changes active session to c2
[+1857.50s] DEBUG: Session c2 is already active
[+1857.52s] DEBUG: Process 4264 exited with return value 0
[+1857.52s] DEBUG: DisplayServer x-1: X server stopped
[+1857.52s] DEBUG: Releasing VT 8
[+1857.52s] DEBUG: DisplayServer x-1: Removing X server authority /run/lightdm/root/:1
[+1857.52s] DEBUG: Seat seat0: Display server stopped

Please let me know if I can provide further logs.

description: updated

This is still affecting me and renders lightdm unusable. It only happens when two external screens are attached.

Just to let you know, active-monitor=cursor eliminates this problem. The standard settings are not working though.

Sean Davis (bluesabre) on 2020-06-14
Changed in lightdm-gtk-greeter:
importance: Undecided → Unknown
status: New → Unknown
Changed in lightdm-gtk-greeter:
status: Unknown → New
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