int restore_node_summary(struct f2fs_sb_info *sbi,
			unsigned int segno, struct f2fs_summary_block *sum)
{
	struct f2fs_node *rn;
	struct f2fs_summary *sum_entry;
	block_t addr;
	int i, idx, last_offset, nrpages;

	/* scan the node segment */
	last_offset = sbi->blocks_per_seg;
	addr = START_BLOCK(sbi, segno);
	sum_entry = &sum->entries[0];

	for (i = 0; i < last_offset; i += nrpages, addr += nrpages) {
		nrpages = min(last_offset - i, BIO_MAX_PAGES);

		/* readahead node pages */
		ra_meta_pages(sbi, addr, nrpages, META_POR, true);

		for (idx = addr; idx < addr + nrpages; idx++) {
			struct page *page = get_tmp_page(sbi, idx);

			rn = F2FS_NODE(page);
			sum_entry->nid = rn->footer.nid;
			sum_entry->version = 0;
			sum_entry->ofs_in_node = 0;
			sum_entry++;
			f2fs_put_page(page, 1);
		}

		invalidate_mapping_pages(META_MAPPING(sbi), addr,
							addr + nrpages);
	}
	return 0;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.