static int page_trans_compound_anon_split(struct page *page)
{
	int ret = 0;
	struct page *transhuge_head = page_trans_compound_anon(page);
	if (transhuge_head) {
		/* Get the reference on the head to split it. */
		if (get_page_unless_zero(transhuge_head)) {
			/*
			 * Recheck we got the reference while the head
			 * was still anonymous.
			 */
			if (PageAnon(transhuge_head))
				ret = split_huge_page(transhuge_head);
			else
				/*
				 * Retry later if split_huge_page run
				 * from under us.
				 */
				ret = 1;
			put_page(transhuge_head);
		} else
			/* Retry later if split_huge_page run from under us. */
			ret = 1;
	}
	return ret;
}

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.