ocfs2/refcounttree: add the missing NULL check of the return value of find_or_create_page()

Add the missing NULL check of the return value of find_or_create_page() in
function ocfs2_duplicate_clusters_by_page().

[akpm@linux-foundation.org: fix layout, per Joel]
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Acked-by: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/refcounttree.c

@@ -2965,6 +2965,11 @@ int ocfs2_duplicate_clusters_by_page(handle_t *handle,
 			to = map_end & (PAGE_CACHE_SIZE - 1);
 
 		page = find_or_create_page(mapping, page_index, GFP_NOFS);
+		if (!page) {
+			ret = -ENOMEM;
+			mlog_errno(ret);
+			break;
+		}
 
 		/*
 		 * In case PAGE_CACHE_SIZE <= CLUSTER_SIZE, This page