Claude review: drm/gem/shmem: Introduce __drm_gem_shmem_free_sgt_locked()

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

Patch Review

**Status: Issue found**

The extracted helper is correct in logic — it moves the unmap/free/kfree sequence into a standalone function that asserts the resv lock is held:

```c
+void __drm_gem_shmem_free_sgt_locked(struct drm_gem_shmem_object *shmem)
+{
+	dma_resv_assert_held(shmem->base.resv);
+
+	dma_unmap_sgtable(shmem->base.dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);
+	sg_free_table(shmem->sgt);
+	kfree(shmem->sgt);
+	shmem->sgt = NULL;
+}
```

**Issue: Kerneldoc name mismatch.** The doc comment says `__drm_gem_shmem_release_sgt_locked` but the function is named `__drm_gem_shmem_free_sgt_locked`:

```c
+ * __drm_gem_shmem_release_sgt_locked - Unpin and DMA unmap pages...
```

This will produce a kernel-doc warning. The V10 changelog mentions "Fix incorrect function name in documentation" but the mismatch persists — it seems the fix was applied in the wrong direction (or partially).

The refactoring of `drm_gem_shmem_release` to call the new helper is correct — the `if (shmem->sgt)` guard is preserved in the caller.

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