static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
			     struct mm_walk *walk)
{
	struct vm_area_struct *vma = walk->vma;
	struct pagemapread *pm = walk->private;
	spinlock_t *ptl;
	pte_t *pte, *orig_pte;
	int err = 0;

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	ptl = pmd_trans_huge_lock(pmdp, vma);
	if (ptl) {
		u64 flags = 0, frame = 0;
		pmd_t pmd = *pmdp;
		struct page *page = NULL;

		if (vma->vm_flags & VM_SOFTDIRTY)
			flags |= PM_SOFT_DIRTY;

		if (pmd_present(pmd)) {
			page = pmd_page(pmd);

			flags |= PM_PRESENT;
			if (pmd_soft_dirty(pmd))
				flags |= PM_SOFT_DIRTY;
			if (pm->show_pfn)
				frame = pmd_pfn(pmd) +
					((addr & ~PMD_MASK) >> PAGE_SHIFT);
		}
#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
		else if (is_swap_pmd(pmd)) {
			swp_entry_t entry = pmd_to_swp_entry(pmd);
			unsigned long offset;

			if (pm->show_pfn) {
				offset = swp_offset(entry) +
					((addr & ~PMD_MASK) >> PAGE_SHIFT);
				frame = swp_type(entry) |
					(offset << MAX_SWAPFILES_SHIFT);
			}
			flags |= PM_SWAP;
			if (pmd_swp_soft_dirty(pmd))
				flags |= PM_SOFT_DIRTY;
			VM_BUG_ON(!is_pmd_migration_entry(pmd));
			page = migration_entry_to_page(entry);
		}
#endif

		if (page && page_mapcount(page) == 1)
			flags |= PM_MMAP_EXCLUSIVE;

		for (; addr != end; addr += PAGE_SIZE) {
			pagemap_entry_t pme = make_pme(frame, flags);

			err = add_to_pagemap(addr, &pme, pm);
			if (err)
				break;
			if (pm->show_pfn) {
				if (flags & PM_PRESENT)
					frame++;
				else if (flags & PM_SWAP)
					frame += (1 << MAX_SWAPFILES_SHIFT);
			}
		}
		spin_unlock(ptl);
		return err;
	}

	if (pmd_trans_unstable(pmdp))
		return 0;
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

	/*
	 * We can assume that @vma always points to a valid one and @end never
	 * goes beyond vma->vm_end.
	 */
	orig_pte = pte = pte_offset_map_lock(walk->mm, pmdp, addr, &ptl);
	for (; addr < end; pte++, addr += PAGE_SIZE) {
		pagemap_entry_t pme;

		pme = pte_to_pagemap_entry(pm, vma, addr, *pte);
		err = add_to_pagemap(addr, &pme, pm);
		if (err)
			break;
	}
	pte_unmap_unlock(orig_pte, ptl);

	cond_resched();

	return err;
}

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.