Track: remove mesa 26.1.1 pin once upstream fixes 26.1.2 GBM crash (amdgpu)

[olafkfreund]

Summary

We carry a surgical pin reverting mesa 26.1.2 → 26.1.1 in overlays/upstream-fixes.nix (PR #891, deployed to p620). This issue tracks removing it once upstream ships a fixed Mesa.

Why the pin exists

gnome-shell/mutter on p620 (amdgpu) was segfaulting repeatedly — 3 crashes in 4 days, accelerating to twice in ~1.5h — each restarting the GNOME session.

Symbolized coredump backtrace:

#0  gbm_bo_destroy             (libgbm 26.0.3)
#1  get_back_bo                (mesa 26.1.2 / libEGL_mesa)
#2  dri2_drm_image_get_buffers
#4  dri2_allocate_textures     (libgallium 26.1.2)
#11 eglMakeCurrent
#13 _cogl_winsys_egl_make_current (mutter 50.1)
#15 maybe_post_next_frame

Root cause

Generation history showed mesa 26.1.1 + libgbm 26.0.3 ran crash-free for weeks. Crashes began only after the system picked up mesa 26.1.2 (nixpkgs bump 14dbea35565, 2026-06-03). libgbm has been 26.0.3 throughout → mesa 26.1.2 is the regression. Both nixos-unstable and master still ship 26.1.2.

Current state

• Pinned to mesa 26.1.1 via overrideAttrs against current build deps; libgbm stays 26.0.3 (the known-good combo).
• Deployed to p620 (current-system = mesa 26.1.1, no 26.1.2 in closure).

Exit condition (when to close)

Remove the mesa override in overlays/upstream-fixes.nix and close this issue when a fixed mesa (≥ 26.1.3, or a 26.1.2 revision carrying the GBM fix) reaches our nixpkgs channel. Verify with /check-updates (watch the mesa delta), then drop the overlay and just test-host p620 before deploy.

References

• Fix PR: fix(mesa): pin mesa to 26.1.1 to stop amdgpu GBM gnome-shell crash #891
• nixpkgs mesa bump that introduced it: 14dbea35565 (mesa: 26.1.1 -> 26.1.2)