https://bugs.kde.org/show_bug.cgi?id=521568
Bug ID: 521568
Summary: KWin Wayland / NVIDIA: "atomic commit failed:
Permission denied" during login transition from SDDM
Wayland to User Session
Classification: Plasma
Product: kwin
Version First 6.6.5
Reported In:
Platform: CachyOS
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: xwayland
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
### System Information
* **OS:** CachyOS (Arch Linux based)
* **KDE Plasma Version:** 6.x (Wayland)
* **KDE Frameworks Version:** 6.x
* **Qt Version:** 6.x
* **Graphics Hardware:** NVIDIA GeForce RTX 5070 Ti (GB203 architecture)
* **Driver Version:** 610.43.02 (Proprietary)
* **Display Manager:** SDDM (configured to run on Wayland with
`kwin_wayland`)
### Description
When logging in from SDDM (which is configured to run on Wayland using
`kwin_wayland`) to a user Plasma Wayland session, the screen goes black and the
monitor loses signal.
Investigation of `journalctl` shows that during the session transition, the
SDDM greeter compositor exits, but the incoming user `kwin_wayland` session
fails to commit frames to the DRM device due to a permission error:
```text
sddm-helper-start-wayland[960]: "kwin_wayland_drm: atomic commit failed:
ζιδΈε€\n"
sddm-helper-start-wayland[960]: Stopping... "kwin_wayland"
```
The system remains running in the background (no signal to display).
**Workaround:**
Pressing `Ctrl + Alt + F3` to switch to TTY3, and then `Ctrl + Alt + F2` to
switch back to the GUI session on TTY2 immediately restores the signal and
displays the desktop. This suggests switching VTs forces a reset or release of
the DRM Master lock, allowing the user's `kwin_wayland` to successfully gain
control.
Changing SDDM's display server back to `x11` completely bypasses this issue,
suggesting a race condition/deadlock in DRM Master transfer between the SDDM
Wayland greeter and the user's Wayland compositor on NVIDIA.
### Steps to Reproduce
1. Configure SDDM to run on Wayland (using `kwin_wayland` as the compositor).
2. Boot the system and reach the login screen.
3. Enter the password and press Enter.
4. Observe the screen going black/losing signal.
5. Switch to TTY3 and back to TTY2 to restore the screen.
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