# DF-1152 — `BUG_ON` kernel panic in amdgpu_dm `dm_update_crtcs_state`

## Result
**NOT REPRODUCED** on this guest. Real source-level defense-in-depth bug;
fix authored.  See `VERDICT.md` for the full analysis.

## Build & run
```
./build.sh    # documents why no executable PoC is possible
./run.sh      # documents why runtime trigger is impossible
```

## Reachability summary
- amdgpu_dm is part of amdgpu, **not** in `X86_64_GENERIC` (0 symbols)
- No AMD GPU on the QEMU guest, no `/dev/dri`
- Trigger needs MST hot-unplug + DRM atomic ioctl on AMD hardware

## Fix
`fix.diff` — strengthen guard at
`sys/dev/drm/amd/display/amdgpu_dm/amdgpu_dm.c:5333` to also require
`dm_new_crtc_state->stream != NULL`.  Applies cleanly with `git apply`.