sddm-greeter segfault

[JohnDoe_71Rus]

after system update i get sddm-greeter segfault and can't login to giu.
but it work in recovery mode

lsb_release -rd
Description: Ubuntu 20.04.1 LTS
Release: 20.04

last lines in log
[ 17.827213] wlan0: associated
[ 17.878225] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
[ 18.073189] show_signal_msg: 15 callbacks suppressed
[ 18.073194] sddm-greeter[930]: segfault at 0 ip 0000000000000000 sp 00007ffe46cdd788 error 14 in sddm-greeter[55cb8623f000+17000]
[ 18.073205] Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
[ 18.306073] Bluetooth: RFCOMM TTY layer initialized
[ 18.306094] Bluetooth: RFCOMM socket layer initialized
[ 18.306104] Bluetooth: RFCOMM ver 1.11
[ 216.160719] sddm-greeter[1267]: segfault at 0 ip 0000000000000000 sp 00007ffd36383ac8 error 14 in sddm-greeter[564c15469000+17000]
[ 216.160732] Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.

i have _usr_bin_sddm.1000.crash - 381 841 byte and _usr_bin_sddm-greeter.119.crash - 2,3Mb
i send it with ubuntu-bug
---
ProblemType: Bug
ApportVersion: 2.20.11-0ubuntu27.14
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: LXQt
DistroRelease: Ubuntu 20.04
Package: sddm 0.18.1-1ubuntu2
PackageArchitecture: amd64
Tags: third-party-packages focal
Uname: Linux 5.8.17-050817-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom davfs2 dialout dip lpadmin plugdev sudo
_MarkForUpload: True

[Chris Guiver (guiverc)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. Please execute the following command only once, as it will automatically gather debugging information, in a terminal:

apport-collect 1909171

When reporting bugs in the future please use apport by using 'ubuntu-bug' and the name of the package affected. You can learn more about this functionality at https://wiki.ubuntu.com/ReportingBugs.

(using a text terminal should allow this to be run, it's likely to want to have you login which is normally done with firefox (which does require a GUI), but please try (I've done it before with lynx I believe instead at terminal)

[JohnDoe_71Rus (johndoe99)]

apport information

[JohnDoe_71Rus (johndoe99)]

apport information

[JohnDoe_71Rus (johndoe99)]

apport information

[JohnDoe_71Rus (johndoe99)]

the problem happened after updating these packages. I don't know how to get this list with text.

[JohnDoe_71Rus (johndoe99)]

part of _usr_bin_sddm-greeter.119.crash without CoreDump

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Remy (remyzerems)]

Hi,

I'm also affected and these are the elements I could gather :
- When the system starts it's showing Lubuntu boot screen, then switches to black screen, then only displays the mouse pointer which I can move. But no other interactions possible. No login interface is loading after that.
I can press Ctrl Alt F4, log in and use startx which works fine.
- The message I have from sddm-greeter is (journalctl extract) :
janv. 19 22:50:20 melanie-cab sddm-greeter[813]: Connected to the daemon.
janv. 19 22:50:20 melanie-cab sddm[611]: Message received from greeter: Connect
janv. 19 22:50:22 melanie-cab kernel: sddm-greeter[813]: segfault at 0 ip 0000000000000000 sp 00007fff17b92968 error 14 in sddm-greeter[55fab6d63000+17000]
janv. 19 22:50:25 melanie-cab sddm-helper[801]: [PAM] Closing session

- Everything was fine before doing the following updates (see apt_history.log)
- Like @johndoe99 it's working correctly if I run in recovery mode (starting recovery mode with advanced tools, then selecting resume). I guessed this way it's setting the system to no GPU mode (GRUB nomodeset) and makes sddm working fine (but wait... no GPU ?? Means no 3D... no gaming... ;-).
- My graphics card is an ATI Radeon (based on the radeon driver). Check lshw_video.log for details.

Could it be coming from a problem with the interaction between sddm and the radeon driver ?

[JohnDoe_71Rus (johndoe99)]

i use the same

Advanced Micro Devices [AMD/ATI]
RS482M [Mobility Radeon Xpress 200]
driver: radeon

Dell inspiron 1501, TL-56

[JohnDoe_71Rus (johndoe99)]

I think this problem is related

[JohnDoe_71Rus (johndoe99)]

Think is mesa 20.2.6+ bug
https://gitlab.freedesktop.org/mesa/mesa/-/issues/3990

[Remy (remyzerems)]

Yes seems to be.
Did you try to downgrade the mesa driver to an older version ? Mine was 20.0.8 before the crashing update came.
It seems that the Focal Fossa LTS is locked to 20.0.4-2... So maybe if we just downgrade to either of these versions we'll get our login screen back !

For now, I do not have the computer at hand so I cannot try that myself...

[JohnDoe_71Rus (johndoe99)]

they can fix the error, but when ...
https://bugs.launchpad.net/ubuntu/+source/mesa/+bug/1915870/comments/18

[rcornet (rcornet)]

I'm also affected by this bug.
There is always a "RIP Code" warning available through dmesg, after crashing of sddm-greeter.

Same graphics:

Advanced Micro Devices [AMD/ATI]
RS482M [Mobility Radeon Xpress 200]
driver: radeon

Acer 5100 with Turion TL-60 CPU

I use Lubuntu.

My work around for anyone wanting something usable is Ctrl-Alt-f2 to the terminal, logging in and installing xdm or wdm, at the end of the installation it lets you choose a new display manager, choose xdm if it is what you installed. And it works, you can log in and use it normally.

I have not tested other Desktops Environments. Everything works under LXqt: 3D Screensaver, Firefox, video playing, etc.

So, If this is a mesa bug, why everything else works? And only sddm-greeter dies?
It stands to reason that sddm-greeter does not do anything more complicated or graphics intensive than Firefox, Mplayer or the 3D screensaver.

[JohnDoe_71Rus (johndoe99)]

just run
glxinfo -B
in therminal.

i use Firefox 86.0.1. next version crash some tabs, i think because new FF use some HW for rendering

[rcornet (rcornet)]

I have another workaround, which actually makes sddm-greeter work again. I had my doubts so I went to confirm my assumptions. You can skip my detective work and rambling by going under the asterisk line.

And it is true that both programs which JohnDoe_71Rus (johndoe99) mentions have similar issues. I haven't looked at glxinfo till now and just now found that pages at unix.stackexchange.com cause tabs crashes with the RIP CODE message in dmesg. But only if I reach to the end of the web page. Strange behavior. Disabling hardware acceleration does not solve the problem.

I mentioned previously that viewing video files was no problem and I tried 'mpv' from the terminal and it uses the gpu driver and works fine, except that it crashes when the video ends with a seg fault. Which is probably why I did not notice the problem when using SMPlayer as the GUI.
Using the vo=xv driver causes no error when finishing the

I suppose that I was just lucky that most webs I visits don't require the magic 3d that makes certain pages crash firefox tabs.

Still sddm-greeter should not fail so catastrophically when it does nothing so complex that requires the gpu's shadow magic. Without terminal-fu level skills most users wont be able to maneuver through the issue. And blindly will blame it on Linux being "unusable".

Some level of fault tolerance is needed but hardware issues are difficult to plan around.

But again: Why sddm-greeter uses gpu's magic?

Dependencies perhaps? Is it Qt5 indirect fault?

Running gdb on sddm on runlevel 2 with no X and the segfault appeared in :
QMessageLogger::fatal(char const*, ...) const () from /lib/x86_64-linux-gnu/libQt5Core.so.5

There is no RIP Code message in dmesg. So I was not convinced.

strace was not helpfull either.

So I gave up on finding the exact culprit. Short of recompiling sddm, qt5 and mesa and debugging them in tandem. Unfortunately I don't have the time.

*********************************************

First: I'm using Lubuntu 20.04, newer *buntu versions I have no idea of their status/compatibility/versioning/etc. This only applies to 20.04.

So I tracked down the main mesa libraries and downgraded them all to the previous version.

#apt install libglapi-mesa=20.0.4-2ubuntu1 libglx-mesa0=20.0.4-2ubuntu1 libgl1-mesa-dri=20.0.4-2ubuntu1 libegl-mesa0=20.0.4-2ubuntu1 libgbm1=20.0.4-2ubuntu1

So then with dpkg-reconfigure sddm-greeter I selected it again as the display manager.

Went to runlevel 5 and presto IT WORKS. Firefox tabs do not crash anymore on unix.stackexchange.com and mpv on the command line using the gpu driver does not segfaults anymore on exit.

So I can confirm without doubt that the main culprit as JohnDoe_71Rus said, is in the mesa libraries upgrade. But I can't confirm the exact code/library where the problem is located.

Surprisingly i did not have any dependencies issues when downgrading this libraries. Other people experience might differ due to the uniqueness of their systems.

To prevent apt from upgrading this packages again;

#apt-mark hold libglapi-mesa=20.0.4-2ubuntu1 libglx-mesa0=20.0.4-2ubuntu1 libgl1-mesa-dri=20.0.4-2ubuntu1 libegl-mesa0=20.0.4-2ubuntu1 libgbm1=20.0.4-2ubuntu1

When...

[Remy (remyzerems)]

Hi guys !

I managed to get it working by upgrading the mesa driver to the latest version using the Kisak-mesa PPA as described there :
https://itsfoss.com/install-mesa-ubuntu/
I followed the paragraph : "Install the latest stable version of Mesa driver in Ubuntu [Latest point release]"

Note that the command "sudo apt install mesa" did not work, so I just did "sudo apt upgrade" instead which installed all the required stuff from the kisak PPA.

It installed the mesa 21.1.0 which is working great on my config. I got the sddm back working (still flickering if I move the mouse to another account, but still working !!).

Seems like the Firefox tabs crash is no longer occurring now (I'm using FF 88.0).

Hope this helps !

[rcornet (rcornet)]

Remy (remyzerems) solution seems better if the PPA author can be trusted.
Part of the security in Linux, comes from not installing random stuff on the Internet.
PPAs are individual repos that anyone can set up without Ubuntu responsability or oversight.

I know nothing about the PPA author, maybe the greatest guy ever.
I just want to remind people of performing due diligence on adding repos from
 unknown/un-trusted sources.

I will stay with the downgraded mesa, since the platform I use is a laptop where everything
I need works right now. Is older hardware, so there is no need for the newest and the
 greatest video card drivers.

I'll wait for the official mesa from ubuntu.

[Remy (remyzerems)]

Dude... I wish you posted that before I started all of these on my side !!
See ?? We both posted nearly at the same time !

I tried to downgrade first but I don't know why it started to throw me huge dependency problems (Qt5 and tons of unknown packages)... I gave up...

Feeling as surprised as you are when I fired up your "mesa downgrading command"... No dependency warnings... Well since it's now working for me, I was not going to play again with those nasty things and going to a possibly new nightmare by pressing "Y" but yeah ! no dependency warning...

rcornet solution seems to be the best/safest one provided there is no dependency warnings.

Cheers