static int f2fs_mpage_readpages(struct address_space *mapping,
			struct list_head *pages, struct page *page,
			unsigned nr_pages, bool is_readahead)
{
	struct bio *bio = NULL;
	sector_t last_block_in_bio = 0;
	struct inode *inode = mapping->host;
	struct f2fs_map_blocks map;
	int ret = 0;

	map.m_pblk = 0;
	map.m_lblk = 0;
	map.m_len = 0;
	map.m_flags = 0;
	map.m_next_pgofs = NULL;
	map.m_next_extent = NULL;
	map.m_seg_type = NO_CHECK_TYPE;
	map.m_may_create = false;

	for (; nr_pages; nr_pages--) {
		if (pages) {
			page = list_last_entry(pages, struct page, lru);

			prefetchw(&page->flags);
			list_del(&page->lru);
			if (add_to_page_cache_lru(page, mapping,
						  page_index(page),
						  readahead_gfp_mask(mapping)))
				goto next_page;
		}

		ret = f2fs_read_single_page(inode, page, nr_pages, &map, &bio,
					&last_block_in_bio, is_readahead);
		if (ret) {
			SetPageError(page);
			zero_user_segment(page, 0, PAGE_SIZE);
			unlock_page(page);
		}
next_page:
		if (pages)
			put_page(page);
	}
	BUG_ON(pages && !list_empty(pages));
	if (bio)
		__submit_bio(F2FS_I_SB(inode), bio, DATA);
	return pages ? 0 : ret;
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.