Claude review: drm/atomic: Add error_code element in atomic_state

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

Patch Review

> +	failure_string = kvasprintf(GFP_ATOMIC, format, varg);
> +
> +	drm_dbg_atomic(state->dev, "Commit failed: %s\n", failure_string);
> +	strscpy_pad(err_code->failure_string, failure_string,
> +		    sizeof(err_code->failure_string));
> +	va_end(varg);

Two bugs here. First, `kvasprintf()` allocates memory that is **never freed with `kfree()`**. Every call to this function leaks memory. Second, if `kvasprintf()` returns NULL (allocation failure), both `drm_dbg_atomic` and `strscpy_pad` will dereference a NULL pointer.

The fix is to add `kfree(failure_string)` after `strscpy_pad`, and to handle the NULL case. Alternatively, since the goal is just to format into a fixed-size buffer, `vsnprintf` directly into `err_code->failure_string` would avoid the allocation entirely and be simpler.

> +	failure_string = kvasprintf(GFP_ATOMIC, format, varg);

`GFP_ATOMIC` is for interrupt/spinlock context. This function is called from ioctl handlers (process context), so `GFP_KERNEL` would be appropriate. But as noted above, the allocation can be avoided entirely.

> +	/* @error_code: pointer to struct holding failure reason and string
> +	 *
> +	 * struct to convey user readable error to the user.
> +	 * Error codes defined in enum drm_mode_atomic_failure_flags
> +	 */
> +	struct drm_mode_atomic_err_code error_code;

The kernel-doc says "pointer to struct" but this is an embedded struct, not a pointer. Also references `drm_mode_atomic_failure_flags` which doesn't exist -- it should be `drm_mode_atomic_failure_codes`. The comment is missing the `/**` kernel-doc opening marker (uses `/*` instead).

Embedding a UAPI struct (`struct drm_mode_atomic_err_code` from `drm_mode.h`) directly in a kernel-internal struct (`struct drm_atomic_state`) is unusual. The UAPI types (`__u64`, `char[]`) are unnecessary for kernel-internal storage. A more conventional approach would be to use kernel types internally and convert when copying to userspace.

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