Update Linux to v5.4.2

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+==========================================
+Distributed Replicated Block Device - DRBD
+==========================================
+
+Description
+===========
+
+  DRBD is a shared-nothing, synchronously replicated block device. It
+  is designed to serve as a building block for high availability
+  clusters and in this context, is a "drop-in" replacement for shared
+  storage. Simplistically, you could see it as a network RAID 1.
+
+  Please visit http://www.drbd.org to find out more.
+
+.. toctree::
+   :maxdepth: 1
+
+   data-structure-v9
+   figures