Claude review: drm/atomic: Allocate atomic_state at the beginning of atomic_ioctl

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

Patch Review

**Issues:**

```c
+	state = drm_atomic_state_alloc(dev);
+	if (!state)
+		return -ENOMEM;
+
+	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
+	state->acquire_ctx = &ctx;
+	state->allow_modeset = !!(arg->flags & DRM_MODE_ATOMIC_ALLOW_MODESET);
+
 	/* disallow for userspace that has not enabled atomic cap (even
 	 * though this may be a bit overkill, since legacy userspace
 	 * wouldn't know how to call this ioctl)
 	 */
 	if (!file_priv->atomic) {
```
- **Performance Regression**: Now allocating state for requests that will immediately fail validation. This wastes memory and CPU cycles for invalid requests.

```c
-	if (arg->reserved) {
-		drm_dbg_atomic(dev, "commit failed: reserved field set\n");
-		ret = -EINVAL;
-		goto out;
-	}
```
- **ABI Change**: Removing the `reserved` field check fundamentally changes the userspace contract. Old userspace that accidentally sets this field will now have different behavior.
- **Backward Compatibility**: This breaks the principle that reserved fields must be zero.

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Generated by Claude Code Patch Reviewer