After upgrading from Debian 13.2 to 13.3, the transition from GDM to the
GNOME session shows a momentary black screen (flash) instead of the
smooth animation that existed before.

* What led up to the situation?
Upgraded from Debian 13.2 to 13.3 (released January 10th, 2026) which
includes mutter and gnome-shell "bugfix releases".

* What exactly did you do (or not do) that was effective (or ineffective)?
Simply logged in via GDM after the upgrade.

* What was the outcome of this action?
Screen goes black for a moment, then the GNOME session appears abruptly.

* What outcome did you expect instead?
Smooth animated transition from GDM greeter to the desktop session,
as it worked in Debian 13.2.

Additional information:
- Reproducible on 2 different machines (desktop and laptop)
- Desktop GPU: AMD Phoenix3 (RDNA3 integrated graphics)
- This is a cosmetic regression, not a blocker

Versions:
mutter-common: 48.7-0+deb13u1
gnome-shell: 48.7-0+deb13u1
gdm3: 48.0-2

I should add that I'm using Wayland, not X11:

$ echo $XDG_SESSION_TYPE
wayland

Looking at the mutter 48.7 changelog, the fixes appear to be X11-related.
This issue may actually be a gnome-shell regression rather than mutter.
Please reassign to gnome-shell if appropriate.

Antonio José Masiá
Software Engineer
ajmasia.dev@ysnp.link
https://betapermanente.link/

--- Rollback test using snapshot.debian.org ---

1. Checked upgrade history to find exact date and versions:

$ zgrep -h "mutter\|gnome-shell" /var/log/dpkg.log* | grep " upgrade "

Result:
2026-01-10 19:13:24 upgrade mutter-common:all 48.4-2 48.7-0+deb13u1
2026-01-10 19:13:25 upgrade gir1.2-mutter-16:amd64 48.4-2 48.7-0+deb13u1
2026-01-10 19:13:25 upgrade libmutter-16-0:amd64 48.4-2 48.7-0+deb13u1
2026-01-10 19:13:25 upgrade mutter-common-bin:amd64 48.4-2 48.7-0+deb13u1
2026-01-10 19:13:25 upgrade gnome-shell-extension-prefs:amd64 48.4-1~deb13u1 48.7-0+deb13u1
2026-01-10 19:13:25 upgrade gnome-shell:amd64 48.4-1~deb13u1 48.7-0+deb13u1
2026-01-10 19:13:25 upgrade gnome-shell-common:all 48.4-1~deb13u1 48.7-0+deb13u1

2. Added Debian snapshot repository (day before upgrade):

$ echo 'deb [check-valid-until=no] https://snapshot.debian.org/archive/debian/20260109T000000Z/ trixie main' | sudo tee /etc/apt/sources.list.d/snapshot.list
$ sudo apt update

3. Downgraded all affected packages:

$ sudo apt install \
mutter-common=48.4-2 \
libmutter-16-0=48.4-2 \
gir1.2-mutter-16=48.4-2 \
mutter-common-bin=48.4-2 \
gnome-shell=48.4-1~deb13u1 \
gnome-shell-common=48.4-1~deb13u1 \
gnome-shell-extension-prefs=48.4-1~deb13u1

4. Held packages to prevent re-upgrade:

$ sudo apt-mark hold mutter-common libmutter-16-0 gir1.2-mutter-16 mutter-common-bin gnome-shell gnome-shell-common gnome-shell-extension-prefs

5. Removed snapshot repository and rebooted:

$ sudo rm /etc/apt/sources.list.d/snapshot.list
$ sudo apt update
$ sudo reboot

--- Result ---

After downgrade to version 48.4, the smooth transition animation from GDM to
GNOME Shell works correctly again. This confirms the regression was introduced in version 48.7-0+deb13u1.

Antonio José Masiá
Software Engineer
ajmasia.dev@ysnp.link
[https://betapermanente.link](https://betapermanente.link/)

---
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Control: severity -1 minor
Control: tags -1 + trixie moreinfo

Not having a perfectly smooth animation is not a serious bug, and we
have plenty of higher priorities. However, this might be related to
other regressions that are more serious (#1125941, #1126174, #1125275)
so it seems worthwhile to investigate.

What graphics hardware is in the laptop? If this is related to the more
serious regressions, then I suspect the answer is going to be some sort
of AMD GPU.

If you look at the system log (systemd Journal) during one of the
startups where the black screen flash existed, are there warning
messages at that time? Specifically, I wonder whether you see

     Page flip failed: drmModeAtomicCommit: Invalid argument

because if you do, that links this to #1125941 and #1126174.

If you upgrade the mutter family of packages back to their versions from
Debian 13.3, but keep the gnome-shell packages held back to 48.4, is
that sufficient to work around this?

What about if you downgrade the mutter family of packages to 48.4, but
upgrade the gnome-shell family to 48.7?

That would tell us whether this is a regression in mutter or in
gnome-shell, which would help to narrow it down.

     smcv

Please try the version from
<https://people.debian.org/~smcv/temp/2026/bug1125941/revert/>
which addresses at least one of those regressions, and perhaps the one
you've reported as well.

     smcv

Hi Simon,

I installed the three packages from your repository:

gnome-shell_48.7-0+deb13u1+1+g122f544e6_amd64.deb
gnome-shell-common_48.7-0+deb13u1+1+g122f544e6_all.deb
gnome-shell-extension-prefs_48.7-0+deb13u1+1+g122f544e6_amd64.deb

After rebooting, the black screen flash during the GDM to GNOME session transition is gone. The issue appears to be fixed.

One additional observation: I'm noticing that it takes more than 10 seconds from unlocking the LUKS-encrypted root partition until GDM appears. Could this be related, or is this expected behavior?

Thank you for the quick response and the patched packages!



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Antonio José Masiá
Software Engineer

ajmasia.dev@ysnp.link • betapermanente.link
🔐 PGP fingerprint:  0F1AE0A0A325682DE8655B406F85F0F75CB8F8D3


Aviso de privacidad. Esta cuenta es de uso personal. No compartas esta dirección sin mi consentimiento. Si recibiste este mensaje por error, infórmame lo antes posible. Si eres el destinatario previsto, trata este mensaje con discreción. Gracias.

Privacy Disclaimer. This is a personal email account. Do not share this address without my consent. If you received this message by mistake, please let me know. If you are the intended recipient, handle this message discreetly. Thank you.

The boot time from LUKS unlock to GDM has been roughly the same across all versions of Debian 13. This is something I've been noticing since I first installed Debian 13 — it didn't happen on Debian 12, where it was noticeably faster.

Antonio José Masiá
Software Engineer

ajmasia.dev@ysnp.link • betapermanente.link
🔐 PGP fingerprint:  0F1AE0A0A325682DE8655B406F85F0F75CB8F8D3


Aviso de privacidad. Esta cuenta es de uso personal. No compartas esta dirección sin mi consentimiento. Si recibiste este mensaje por error, infórmame lo antes posible. Si eres el destinatario previsto, trata este mensaje con discreción. Gracias.

Privacy Disclaimer. This is a personal email account. Do not share this address without my consent. If you received this message by mistake, please let me know. If you are the intended recipient, handle this message discreetly. Thank you.

We believe that the bug you reported is fixed in the latest version of
gnome-shell, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1125273@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Simon McVittie <smcv@debian.org> (supplier of updated gnome-shell package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Tue, 27 Jan 2026 16:42:32 +0000
Source: gnome-shell
Architecture: source
Version: 49.3-1
Distribution: unstable
Urgency: medium
Maintainer: Debian GNOME Maintainers <pkg-gnome-maintainers@lists.alioth.debian.org>
Changed-By: Simon McVittie <smcv@debian.org>
Closes: 1125273 1125275 1125941 1126174
Changes:
 gnome-shell (49.3-1) unstable; urgency=medium
 .
   * Team upload
   * New upstream release
   * d/p/Revert-main-Register-session-with-GDM-on-startup.patch:
     Revert a change that shouldn't have been backported to 49.x.
     Upstream suggested this as a possible trigger for regressions in
     modesetting during first login on some systems (the regression seems to
     be specific to AMD GPUs, but not all AMD GPUs are affected) and it
     seems that it was developed for v50, under the assumption that gdm3
     changes from v50 would be present.
     For whatever reason (possibly timing-dependent), this was reported
     in Debian 13 but not in testing/unstable.
     (Closes: #1125941, #1125273, #1125275, #1126174)
   * d/control: Reinstate direct Build-Depends on the dbus-daemon package.
     gnome-shell's test suite explicitly invokes dbus-run-session, which
     is in the dbus-daemon package. If the dependency had been on dbus, that
     would have been incompatible with dbus-broker, but a test dependency
     on dbus-daemon is fine.
   * d/patches/series: Sort with closest-to-upstream first.
     No functional change.
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We believe that the bug you reported is fixed in the latest version of
gnome-shell, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1125273@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Simon McVittie <smcv@debian.org> (supplier of updated gnome-shell package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Sat, 07 Feb 2026 11:16:25 +0000
Source: gnome-shell
Architecture: source
Version: 48.7-0+deb13u2
Distribution: trixie
Urgency: medium
Maintainer: Debian GNOME Maintainers <pkg-gnome-maintainers@lists.alioth.debian.org>
Changed-By: Simon McVittie <smcv@debian.org>
Closes: 1125273 1125275 1125941 1126174
Changes:
 gnome-shell (48.7-0+deb13u2) trixie; urgency=medium
 .
   * Team upload
   * d/p/Revert-main-Register-session-with-GDM-on-startup.patch:
     Revert an upstream change that was not intended to be backported
     to 48.x. A corresponding revert has been queued for inclusion in
     48.8 upstream.
     The change was developed for v50, under the assumption that gdm3
     changes from v50 would be present, but then mistakenly backported
     to 48.x and included in the 48.7 release.
     The resulting change to timings/sequencing triggered regressions in
     modesetting during first login on some systems, which can result in
     the Shell UI never appearing.
     (Closes: #1125941, #1125273, #1125275, #1126174)
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Git-Tag-Info: tag=0026dfa900d24db5e7d1fd116abb06cacdccf359 fp=7a073ad1ae694fa25bff62e5235c099d3eb33076
Git-Tag-Tagger: Simon McVittie <smcv@debian.org>
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