> On Sep 24, 2024, at 15:29, Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
>
>
>
> On 2024/9/24 15:14, Muchun Song wrote:
>>> 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.
>
> My bad, should set nr_ptes to 0 and call flush_tlb_mm() here, right?
Or add a new label "out" just below the "abort". Then go to out.
>
>>> + }
>>> + }
>>> }
>>> 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);
>
> Both are fine, will do.
>
> Thanks,
> Qi
>
>>>
>>> mmu_notifier_invalidate_range_end(&range);
>>> --
>>> 2.20.1
