diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 58a7e3bbe130..713f4336107f 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -90,6 +90,11 @@
  *
  * Finally iteration helpers to walk all nodes and all holes are provided as are
  * some basic allocator dumpers for debugging.
+ *
+ * Note that this range allocator is not thread-safe, drivers need to protect
+ * modifications with their on locking. The idea behind this is that for a full
+ * memory manager additional data needs to be protected anyway, hence internal
+ * locking would be fully redundant.
  */
 
 static struct drm_mm_node *drm_mm_search_free_in_range_generic(const struct drm_mm *mm,