Ubuntu 24.04: gnome-shell crashes on Xorg if a legacy X11 cursor theme is selected

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Hello, i have the exact same issue. After crashing I switched to a Wayland Session and I noticed the cursor was also bugged (white square) when hovering over the dock

Both that crash:

Apr 19 09:25:50 Legion5Pro gnome-shell[2799]: No cursor theme available, please install a cursor theme
Apr 19 09:25:50 Legion5Pro gnome-shell[2799]: Received an X Window System error.
                                              This probably reflects a bug in the program.
                                              The error was 'BadCursor (invalid Cursor parameter)'.
                                                (Details: serial 127343 error_code 6 request_code 95 (core protocol) minor_code 0)
                                                (Note to programmers: normally, X errors are reported asynchronously;
                                                 that is, you will receive the error a while after causing it.
                                                 To debug your program, run it with the MUTTER_SYNC environment
                                                 variable to change this behavior. You can then get a meaningful
                                                 backtrace from your debugger if you break on the mtk_x_error() function.)
Apr 19 09:25:50 Legion5Pro gnome-shell[2799]: GNOME Shell crashed with signal 5
Apr 19 09:25:50 Legion5Pro gnome-shell[2799]: == Stack trace for context 0x5bbb2d7c8930 ==
Apr 19 09:25:50 Legion5Pro gnome-shell[2799]: #0 5bbb2d890098 i resource:///org/gnome/shell/ui/init.js:21 (13ed08470bf0 @ 48)

and the white square:

https://gitlab.gnome.org/GNOME/mutter/-/issues/3184

seem to be due to mutter 46 not supporting legacy X11 cursor themes.

FWIW, I am also affected in wayland, all packages up-to-date. Changing the cursor to adwaita fixes it for me was in DMZ-black).

Attaching a screenshot of what I am looking at when using DMZ-black

Well I found a solution when I downloaded the breeze theme I got breeze-cursor instead of a white square when I use dmz-white in wayland when I move the cursor to dash to panel. It is also the default cursor in xorg.

How it works? Like this:
There is a default folder in /usr/share/icons
There is index.theme inside

There is a line that indicates
Inherits=breeze_cursors

Basically you need to create a new cross cursor that would indicate that there is no cursor or supply the sudo apt-get install breeze package by default for Ubuntu
Or that it points somehow to the yaru cursor, only I do not know how to do it because breeze_cursors is a separate folder.
Well, the course of my idea you have understood

vadim, why couldn't you inherit Yaru or Adwaita which are already installed?

I don't know how to write the path to the cursor file
breeze cursors is a separate folder
And the cursor in the yaru is in /Yaru/cursors
I tried to write the full path there and it didn’t work, I don’t know how to write the path to the cursor

Likely upstream bug: https://gitlab.gnome.org/GNOME/mutter/-/issues/3454

Confirmed:

#6 0x00007da91c9077fb in _XError () at /lib/x86_64-linux-gnu/libX11.so.6
#7 0x00007da91c90790f in ??? () at /lib/x86_64-linux-gnu/libX11.so.6
#8 0x00007da91c9079cd in ??? () at /lib/x86_64-linux-gnu/libX11.so.6
#9 0x00007da91c90971d in _XReply () at /lib/x86_64-linux-gnu/libX11.so.6
#10 0x00007da91c909aa5 in XSync () at /lib/x86_64-linux-gnu/libX11.so.6
#11 0x00007da91c909b3f in ??? () at /lib/x86_64-linux-gnu/libX11.so.6
#12 0x00007da91c8e0b2d in XFreeCursor () at /lib/x86_64-linux-gnu/libX11.so.6
#13 0x00007da91cf73c85 in meta_cursor_renderer_x11_update_cursor
    (renderer=0x5f58cdeed1a0, cursor_sprite=0x5f58cdc29790)
    at ../src/backends/x11/meta-cursor-renderer-x11.c:113
#14 0x00007da91cec592f in meta_cursor_renderer_update_cursor
    (renderer=0x5f58cdeed1a0, cursor_sprite=0x5f58cdc29790)
    at ../src/backends/meta-cursor-renderer.c:425
#15 0x00007da91cec5a3c in meta_cursor_renderer_force_update
    (renderer=0x5f58cdeed1a0) at ../src/backends/meta-cursor-renderer.c:460
#16 0x00007da91cf7121e in meta_backend_x11_reload_cursor (x11=0x5f58cdc05470)
    at ../src/backends/x11/meta-backend-x11.c:1121
#17 0x00007da91cfa0754 in update_cursor_theme (x11_display=0x5f58cdfd9b30)
    at ../src/x11/meta-x11-display.c:1757
#18 0x00007da91dbb86bd in ??? () at /lib/x86_64-linux-gnu/libgobject-2.0.so.0
#19 0x00007da91dbb87c1 in g_signal_emit_valist ()
    at /lib/x86_64-linux-gnu/libgobject-2.0.so.0

In progress: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3718

I've also encountered this bug/crash since I always change the cursor to DMZ-White when I install Ubuntu and I reckon other ex-Windows users might also do. Before that I've noticed this weird "X" cursor when desktop was loading (see attachement).
I've replicated the bug using only the live USB (try without installing Ubuntu 24.04). Just apt install gnome-tweaks and then change cursor to DMZ-White leads to crashing. Re-tried by first installing Nvidia drivers with no difference.

Please only use CSS cursor themes (like Yaru or Adwaita) until this bug is fixed.

Thanks for identifying the cause. I had to use wayland, and now I can go back to Xorg. For me it was impossible to find out why this was happening, because I was using DMZ-black, and upgraded from 22.04 much before if was stable. So I thought it will be resolved by the time of 24.04 launch. Unfortunately, that did not happen. Also had to find a substitute for a program I use, and it only works in X.

I got the same issue at the GDM. GDM uses X with nvidia driver and also uses Yaru cursor theme, which wasn't present in my system.

I upgraded from 22.04 to 24.04 and could no longer log in. Just immediately got the sad computer face screen. Can confirm that installing `breeze` fixed this. I don't really know what's going on but it seems to provide a functional fallback for when the selected cursor theme isn't working. Trying to explicitly change the cursor theme with dconf did not fix the problem, but installing breeze got me going again.

A further update -- a bit of a hack, but, I liked my "whiteglass" cursor, and I found that copying its left_ptr and right_ptr files from /usr/share/icons/whiteglass/cursors overtop of the corresponding ones in /usr/share/icons/Breeze_Snow/cursors gave me back my whiteglass cursor, at least for the pointer. :-P (I made backups of the originals before doing this.) Except in Firefox for some reason. Anyway, I don't see this as a long-term solution, but it at least helps somewhat with visibility for me.