static struct page *can_gather_numa_stats_pmd(pmd_t pmd,
					      struct vm_area_struct *vma,
					      unsigned long addr)
{
	struct page *page;
	int nid;

	if (!pmd_present(pmd))
		return NULL;

	page = vm_normal_page_pmd(vma, addr, pmd);
	if (!page)
		return NULL;

	if (PageReserved(page))
		return NULL;

	nid = page_to_nid(page);
	if (!node_isset(nid, node_states[N_MEMORY]))
		return NULL;

	return page;
}

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.