Dear maintainers,

after upgrading mutter and gnome-shell to 51.0-3 (Debian sid, 2026-10-22),
GDM can no longer start a greeter and the GNOME session crashes at startup
on a system using the proprietary NVIDIA driver shipped in testing/sid
(550.163.01-5.1).

Symptoms

- gdm retries until "GdmLocalDisplayFactory: maximum number of display
  failures reached. Giving up."
- gnome-shell[3916]: segfault at ... ip ... sp ... error 4 in
  libmutter-cogl-51.so.0.0.0[5faf4]
- org.gnome.Shell@gdm.service: Main process exited, code=killed,
  status=11/SEGV
- GdmDisplay: Session never registered, failing

Reproduction (deterministic, without GDM)

  $ gnome-shell --headless --mode=user; echo $?
  139
  $ gnome-shell --headless --mode=gdm; echo $?
  139

strace shows the NVIDIA EGL/GBM stack being loaded (renderD129,
nvidia-drm_gbm.so, libEGL_nvidia.so) followed by SIGSEGV. The faulting
offset 0x5faf4 corresponds to cogl_renderer_is_hardware_accelerated(),
which dereferences a NULL renderer. Upstream mutter 51 removed support for
legacy NVIDIA drivers (NEWS 51.alpha, MR !5079); whether 550 counts as
legacy is unclear, but mutter should not segfault when renderer/EGL
initialization fails.

System

- Debian sid/testing (forky), kernel 7.1.13+deb14-amd64
- mutter 51.0-3, gnome-shell 51.0-3, gdm3 51.1-1
- nvidia-driver 550.163.01-5.1, GeForce RTX 3070 Ti Laptop GPU
- Downgrading mutter/gnome-shell to 50.5-1 (testing) makes GNOME work again

Impact

550.163.01 is the newest nvidia-driver in testing and sid; 555.58.02 has
been in experimental since 2024. When mutter 51 migrates to testing, GNOME
will be unusable for users of the packaged NVIDIA driver.

Please consider:

1. keeping mutter 51 out of testing until a compatible driver is
   available, or
2. adding a versioned Breaks/Conflicts against nvidia-driver (<< 555) so
   apt cannot install the broken combination, and/or
3. fixing the NULL dereference so an EGL failure degrades gracefully
   instead of killing gnome-shell.

Thanks,
Claudio Giordano

Control: affects -1 src:nvidia-graphics-drivers

Did you try the nvidia drivers from Experimental?

Thank you,
Jeremy Bícha

Control: forwarded -1 https://gitlab.gnome.org/GNOME/mutter/-/work_items/5074

I don't think it necessarily does.
<https://gitlab.gnome.org/GNOME/mutter/-/work_items/4279> mentions that
EGLStream (the legacy mechanism that was removed) was needed for the
v470 driver, but no longer necessary for newer drivers.

(The NVIDIA proprietary driver in Debian is known to be out of date,
<https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1081302> etc., but
that isn't necessarily the issue here.)

Another possible root cause is that if your laptop combines an NVIDIA
discrete GPU with an Intel or AMD integrated GPU, and there are
power-management or hybrid-graphics workarounds in use to force GNOME
Shell to render on the less-power-consuming integrated GPU, this is
known to result in a similar crash:
https://gitlab.gnome.org/GNOME/mutter/-/work_items/5074
https://gitlab.gnome.org/GNOME/mutter/-/work_items/5074, happening for
either the same reason or a different reason. If so, it has a potential
fix proposed upstream, although the code is not quite right yet
<https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/5355>.

Please could you get a backtrace from the crash? See:
https://wiki.debian.org/HowToGetABacktrace

Can you confirm that the version 555 driver (in experimental) does work?
Adding this Breaks/Replaces would only be useful if it does actually
exclude the drivers that don't work.

This is <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/5355>
upstream.

     smcv

Idk why Debian thinks one size fits all is a good approach for complex GPU
drivers and firmwares. Official Nvidia Unix Versions have move passed 550
over a year ago, current unix stable version is at 595.113.07 and nvidia
itself recommends gpu owners to use it's new feature branch 615.x.x series
for latest features + better performance.

What should they do instead?

Either keep it updated or drop proprietary Nvidia drivers from repo
altogether. Users can install  themselves if they need.

I tried to reproduced the issue on my laptop with duel gpu ( intel +
Nvidia) and in my desktop with Nvidia only gpu. Yes it's indeed a duel gpu
issue.
Both on v615 driver. laptop crashes with same SEGV other one doesn't.