Comment 1 for bug 1801246

Fix added in 4.19-rc6:

commit 41c9b1be335b5afc3b5fb71c5d16f9d5939cd13f
Author: Dave Jiang <email address hidden>
Date: Mon Sep 10 16:18:29 2018 -0700

device-dax: Add missing address_space_operations

With address_space_operations missing for device dax, namely the
.set_page_dirty, we hit a kernel warning when running destructive
ndctl unit test: make TESTS=device-dax check

WARNING: CPU: 3 PID: 7380 at fs/buffer.c:581 __set_page_dirty+0xb1/0xc0

Setting address_space_operations to noop_set_page_dirty and
noop_invalidatepage for device dax to prevent fallback to
__set_page_dirty_buffers() and block_invalidatepage() respectively.

Fixes: 2232c6382a ("device-dax: Enable page_mapping()")

Acked-by: Jeff Moyer <email address hidden>
Reported-by: Vishal Verma <email address hidden>
Signed-off-by: Dave Jiang <email address hidden>
Signed-off-by: Dan Williams <email address hidden>