ceph: remove bogus checks and WARN_ONs from ceph_set_page_dirty

The checks for page->mapping are odd, as set_page_dirty is an
address_space operation, and I don't see where it would be called on a
non-pagecache page.

The warning about the page lock also seems bogus.  The comment over
set_page_dirty() says that it can be called without the page lock in
some rare cases. I don't think we want to warn if that's the case.
Reported-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/addr.c

@@ -82,10 +82,6 @@ static int ceph_set_page_dirty(struct page *page)
 	struct inode *inode;
 	struct ceph_inode_info *ci;
 	struct ceph_snap_context *snapc;
-	int ret;
-
-	if (unlikely(!mapping))
-		return !TestSetPageDirty(page);
 
 	if (PageDirty(page)) {
 		dout("%p set_page_dirty %p idx %lu -- already dirty\n",
@@ -130,11 +126,7 @@ static int ceph_set_page_dirty(struct page *page)
 	BUG_ON(PagePrivate(page));
 	attach_page_private(page, snapc);
 
-	ret = __set_page_dirty_nobuffers(page);
-	WARN_ON(!PageLocked(page));
-	WARN_ON(!page->mapping);
-
-	return ret;
+	return __set_page_dirty_nobuffers(page);
 }
 
 /*