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Bug 2151128 - Unable to access session via xdmcp
Summary: Unable to access session via xdmcp
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 8
Classification: Red Hat
Component: mesa
Version: 8.8
Hardware: x86_64
OS: Linux
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Dave Airlie
QA Contact: Desktop QE
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2022-12-06 08:20 UTC by Michal Odehnal
Modified: 2023-05-16 09:55 UTC (History)
4 users (show)

Fixed In Version: mesa-22.3.0-1.el8
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2023-05-16 08:35:54 UTC
Type: Bug
Target Upstream Version:
Embargoed:
pm-rhel: mirror+

Attachments (Terms of Use)
journal log (272.33 KB, text/plain)
2022-12-06 08:20 UTC, Michal Odehnal 		no flags Details
Initialize shm opcode (2.51 KB, patch)
2022-12-06 18:19 UTC, Ray Strode [halfline] 		no flags Details | Diff
View All


Links
System ID Private Priority Status Summary Last Updated
Red Hat Issue Tracker RHELPLAN-141390 0 None None None 2022-12-06 08:23:05 UTC
Red Hat Product Errata RHBA-2023:2824 0 None None None 2023-05-16 08:36:28 UTC
freedesktop.org Gitlab mesa mesa merge_requests 20188 0 None opened glx: fix xshm check to init xshm_opcode. 2022-12-06 19:45:52 UTC

Description Michal Odehnal 2022-12-06 08:20:56 UTC 
Created attachment 1930369 [details]
journal log

Description of problem:
When using Xephyr to access local session via xdmcp, nothing happens, only black screen.

Version-Release number of selected component (if applicable):
gdm-40.0-25.el8.x86_64
gnome-shell-3.32.2-50.el8.x86_64
xorg-x11-server-Xephyr-1.20.11-10.el8.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Xephyr :99 -query localhost -fullscreen
2.
3.

Actual results:
Black screen.

Expected results:
Login screen loads.

Additional info:
$ cat /etc/gdm/custom.conf
[daemon]
WaylandEnable=false
AutomaticLoginEnable = true
AutomaticLogin = test
[security]

[xdmcp]
Enable=true
[chooser]

[debug]
Enable=true

What jumps out to me is the line: "Cannot use session '/usr/share/gdm/greeter/gnome-session/sessions/gnome-login.session': non-existing or invalid file" which might be relevant since the login screen does not load.
Comment 3 Ray Strode [halfline] 2022-12-06 15:15:26 UTC 
this seems to be a mesa regression of some sort following a rebase.

The login screen is there, it's just not painting. The mouse cursor even changes when hovering over where the password field should be.


It happens when going from mesa-22.1.5-2.el8 to mesa-22.3.0-0.4.rc4.el8
Comment 4 Ray Strode [halfline] 2022-12-06 15:29:53 UTC 
hmm it's not a problem with software rendering apparently. Xephyr works fine with glxgears and with mutter even, so it seems like it's a problem specific to remote x servers. maybe some sort of shm issue?
Comment 5 Olivier Fourdan 2022-12-06 15:46:59 UTC 
(In reply to Ray Strode [halfline] from comment #4)
> hmm it's not a problem with software rendering apparently. Xephyr works fine
> with glxgears and with mutter even, so it seems like it's a problem specific
> to remote x servers. maybe some sort of shm issue?

See if the patch I posted in bug 2092450 helps here.
Comment 6 Ray Strode [halfline] 2022-12-06 16:37:36 UTC 
it seems to a problem with shm detection.

 Xephyr -extension mit-shm -query localhost :123

makes it work. So I guess it's trying to use XShmPutImage over a tcp display connection.
Comment 7 Ray Strode [halfline] 2022-12-06 17:36:54 UTC 
One issue I've noticed just reading through the code is here:

https://gitlab.freedesktop.org/mesa/mesa/-/commit/68e89401140d1b3a17052899c54577de3f008b67

xshm_opcode is a global variable used in error handlers and it's no longer getting initialized. that might be the problem.
Comment 8 Ray Strode [halfline] 2022-12-06 18:19:42 UTC 
Created attachment 1930524 [details]
Initialize shm opcode

yea i did a scratch build here:

https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=49445676

with the obvious change and that fixed it.
Comment 10 Michal Odehnal 2022-12-07 14:10:13 UTC 
This fixes the issue for me too.
Comment 17 errata-xmlrpc 2023-05-16 08:35:54 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (mesa bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2023:2824
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