Claude review: drm/amdgpu: fix root reservation in amdgpu_vm_handle_fault

[Claude Code Review Bot <claude-review@example.com>]

Overall Series Review

Subject: drm/amdgpu: fix root reservation in amdgpu_vm_handle_fault
Author: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Patches: 2
Reviewed: 2026-04-23T09:58:50.258731

---

This is a single-patch fix for a real deadlock in `amdgpu_vm_handle_fault`. The bug: `amdgpu_vm_lock_by_pasid` acquires the root BO reservation (via `amdgpu_bo_reserve`), then calls `svm_range_restore_pages`, which eventually reaches `svm_range_reserve_bos` → `amdgpu_vm_lock_pd`, trying to lock the same root BO via `drm_exec`. Since the first lock is held without a `ww_acquire_ctx` (NULL) and the second attempts to lock with a `drm_exec` context, the same thread deadlocks on the `ww_mutex`.

The fix — unreserve root before calling `svm_range_restore_pages`, then re-acquire via `amdgpu_vm_lock_by_pasid` if needed — is the correct minimal approach. The unlock/relock window is properly guarded by the re-validation in `amdgpu_vm_lock_by_pasid` (which re-checks the pasid→vm mapping and verifies `vm->root.bo` still matches).

**Verdict: The patch is correct and should be safe to apply.** One minor concern noted below about a missing `Cc: stable` tag.

---
Generated by Claude Code Patch Reviewer