static int f2fs_write_node_pages(struct address_space *mapping,
			    struct writeback_control *wbc)
{
	struct f2fs_sb_info *sbi = F2FS_M_SB(mapping);
	struct blk_plug plug;
	long diff;

	/* balancing f2fs's metadata in background */
	f2fs_balance_fs_bg(sbi);

	/* collect a number of dirty node pages and write together */
	if (get_pages(sbi, F2FS_DIRTY_NODES) < nr_pages_to_skip(sbi, NODE))
		goto skip_write;

	trace_f2fs_writepages(mapping->host, wbc, NODE);

	diff = nr_pages_to_write(sbi, NODE, wbc);
	wbc->sync_mode = WB_SYNC_NONE;
	blk_start_plug(&plug);
	sync_node_pages(sbi, wbc);
	blk_finish_plug(&plug);
	wbc->nr_to_write = max((long)0, wbc->nr_to_write - diff);
	return 0;

skip_write:
	wbc->pages_skipped += get_pages(sbi, F2FS_DIRTY_NODES);
	trace_f2fs_writepages(mapping->host, wbc, NODE);
	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.