Claude review: drm/gem: Make the GEM LRU lock part of drm_device

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Overall Series Review

Subject: drm/gem: Make the GEM LRU lock part of drm_device
Author: Boris Brezillon <boris.brezillon@collabora.com>
Patches: 5
Reviewed: 2026-05-16T14:06:15.229271

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This is a single patch (v3, distilled from an earlier 4-patch series) that addresses a real race condition in the DRM GEM LRU shrinker infrastructure. The race is between `drm_gem_lru_remove()` and `drm_gem_lru_scan()`: the old code reads `obj->lru` without the lock, dereferences it to get `lru->lock`, then takes that lock — but `obj->lru` can change (or become NULL) between the read and the lock acquisition. Since `drm_gem_lru_scan()` uses a stack-allocated `still_in_lru`, this can result in a use-after-free.

The fix is clean and well-motivated: move the lock from `struct drm_gem_lru` to `struct drm_device`, eliminating the chicken-and-egg problem entirely. The commit message clearly explains the rationale and acknowledges the trade-off (coarser locking, with a path to finer-grained locking if ever needed). The patch already has Reviewed-by tags from Rob Clark (MSM maintainer) and Liviu Dudau.

**Verdict: This patch looks correct and is ready to merge.** I have only minor observations below.

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