> On Sep 24, 2024, at 16:57, Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
>
>
>
> On 2024/9/24 16:52, Muchun Song wrote:
>>> 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.
>
> For this way, we also need to call flush_tlb_mm() first, like the
> following:
>
> if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd)))) {
> spin_unlock(pml);
> flush_tlb_mm(mm);
> goto out;
> }
Fine.
>
>>>
>>>>> + }
>>>>> + }
>>>>> }
>>>>> 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
