diff --git a/Documentation/block/null_blk.txt b/Documentation/block/null_blk.txt
index fcf7f8487d8e..733927a7b501 100644
--- a/Documentation/block/null_blk.txt
+++ b/Documentation/block/null_blk.txt
@@ -77,3 +77,8 @@ use_lightnvm=[0/1]: Default: 0
 no_sched=[0/1]: Default: 0
   0: nullb* use default blk-mq io scheduler.
   1: nullb* doesn't use io scheduler.
+
+shared_tags=[0/1]: Default: 0
+  0: Tag set is not shared.
+  1: Tag set shared between devices for blk-mq. Only makes sense with
+     nr_devices > 1, otherwise there's no tag set to share.