static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
			   struct mm_walk *walk)
{
	struct vm_area_struct *vma = walk->vma;
	pte_t *pte;
	spinlock_t *ptl;

	ptl = pmd_trans_huge_lock(pmd, vma);
	if (ptl) {
		if (pmd_present(*pmd))
			smaps_pmd_entry(pmd, addr, walk);
		spin_unlock(ptl);
		goto out;
	}

	if (pmd_trans_unstable(pmd))
		goto out;
	/*
	 * The mmap_sem held all the way back in m_start() is what
	 * keeps khugepaged out of here and from collapsing things
	 * in here.
	 */
	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
	for (; addr != end; pte++, addr += PAGE_SIZE)
		smaps_pte_entry(pte, addr, walk);
	pte_unmap_unlock(pte - 1, ptl);
out:
	cond_resched();
	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.