> On Sep 24, 2024, at 14:11, Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
> In collapse_pte_mapped_thp(), we may modify the pte and pmd entry after
> acquring the ptl, so convert it to using pte_offset_map_rw_nolock(). At
> this time, the pte_same() check is not performed after the PTL held. So we
> should get pgt_pmd and do pmd_same() check after the ptl held.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> ---
> mm/khugepaged.c | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 6498721d4783a..8ab79c13d077f 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1605,7 +1605,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED))
> pml = pmd_lock(mm, pmd);
>
> - start_pte = pte_offset_map_nolock(mm, pmd, haddr, &ptl);
> + start_pte = pte_offset_map_rw_nolock(mm, pmd, haddr, &pgt_pmd, &ptl);
> if (!start_pte) /* mmap_lock + page lock should prevent this */
> goto abort;
> if (!pml)
> @@ -1613,6 +1613,9 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> else if (ptl != pml)
> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
>
> + if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd))))
> + goto abort;
> +
> /* step 2: clear page table and adjust rmap */
> for (i = 0, addr = haddr, pte = start_pte;
> i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
> @@ -1645,7 +1648,6 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> nr_ptes++;
> }
>
> - pte_unmap(start_pte);
> if (!pml)
> spin_unlock(ptl);
>
> @@ -1658,13 +1660,19 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> /* step 4: remove empty page table */
> if (!pml) {
> pml = pmd_lock(mm, pmd);
> - if (ptl != pml)
> + if (ptl != pml) {
> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
> + if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd)))) {
> + spin_unlock(pml);
> + goto abort;
Drop the reference of folio and the mm counter twice at the label of abort and the step 3.
> + }
> + }
> }
> pgt_pmd = pmdp_collapse_flush(vma, haddr, pmd);
> pmdp_get_lockless_sync();
> if (ptl != pml)
> spin_unlock(ptl);
> + pte_unmap(start_pte);
> spin_unlock(pml);
Why not?
pte_unmap_unlock(start_pte, ptl);
if (pml != ptl)
spin_unlock(pml);
>
> mmu_notifier_invalidate_range_end(&range);
> --
> 2.20.1
