static struct page *page_trans_compound_anon(struct page *page)
{
	if (PageTransCompound(page)) {
		struct page *head = compound_trans_head(page);
		/*
		 * head may actually be splitted and freed from under
		 * us but it's ok here.
		 */
		if (PageAnon(head))
			return head;
	}
	return NULL;
}

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.