ocfs2: Fix deadlock when allocating page

We cannot call grab_cache_page() when holding filesystem locks or with
a transaction started as grab_cache_page() calls page allocation with
GFP_KERNEL flag and thus page reclaim can recurse back into the filesystem
causing deadlocks or various assertion failures. We have to use
find_or_create_page() instead and pass it GFP_NOFS as we do with other
allocations.

Acked-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Tao Ma <tao.ma@oracle.com>

fs/ocfs2/refcounttree.c

@@ -2960,7 +2960,7 @@ static int ocfs2_duplicate_clusters_by_page(handle_t *handle,
 		if (map_end & (PAGE_CACHE_SIZE - 1))
 			to = map_end & (PAGE_CACHE_SIZE - 1);
 
-		page = grab_cache_page(mapping, page_index);
+		page = find_or_create_page(mapping, page_index, GFP_NOFS);
 
 		/*
 		 * In case PAGE_CACHE_SIZE <= CLUSTER_SIZE, This page
@@ -3179,7 +3179,8 @@ static int ocfs2_cow_sync_writeback(struct super_block *sb,
 		if (map_end > end)
 			map_end = end;
 
-		page = grab_cache_page(context->inode->i_mapping, page_index);
+		page = find_or_create_page(context->inode->i_mapping,
+					   page_index, GFP_NOFS);
 		BUG_ON(!page);
 
 		wait_on_page_writeback(page);