Miaohe Lin <linmiaohe@xxxxxxxxxx> writes:
> On 2022/3/7 13:37, Huang, Ying wrote:
>> Miaohe Lin <linmiaohe@xxxxxxxxxx> writes:
>>
>>> __migration_entry_wait and migration_entry_wait_on_locked assume pte is
>>> always mapped from caller. But this is not the case when it's called from
>>> migration_entry_wait_huge and follow_huge_pmd. And a parameter unmap to
>>> indicate whether pte needs to be unmapped to fix this issue.
>>
>> This seems a possible issue.
>>
>> Have you tested it? It appears that it's possible to trigger the
>> issue. If so, you can paste the error log here.
>
> This might happen iff on x86 machine with HIGHMEM enabled which is uncommon
> now (at least in my work environment).
Yes. 32-bit isn't popular now. But you can always test it via virtual
machine.
> So I can't paste the err log. And The
> issues from this series mainly come from the code investigating with some tests.
If not too complex, I still think it's better to test your code and
verify the problem.
Best Regards,
Huang, Ying
> Thanks. :)
>
>>
>> BTW: have you tested the other functionality issues in your patchset?
>>
>> Best Regards,
>> Huang, Ying
>>
>>> Fixes: 30dad30922cc ("mm: migration: add migrate_entry_wait_huge()")
>>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>>> ---
>>> include/linux/migrate.h | 2 +-
>>> include/linux/swapops.h | 4 ++--
>>> mm/filemap.c | 10 +++++-----
>>> mm/hugetlb.c | 2 +-
>>> mm/migrate.c | 14 ++++++++------
>>> 5 files changed, 17 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
>>> index 66a34eae8cb6..3ef4ff699bef 100644
>>> --- a/include/linux/migrate.h
>>> +++ b/include/linux/migrate.h
>>> @@ -41,7 +41,7 @@ extern int migrate_huge_page_move_mapping(struct address_space *mapping,
>>> extern int migrate_page_move_mapping(struct address_space *mapping,
>>> struct page *newpage, struct page *page, int extra_count);
>>> void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
>>> - spinlock_t *ptl);
>>> + spinlock_t *ptl, bool unmap);
>>> void folio_migrate_flags(struct folio *newfolio, struct folio *folio);
>>> void folio_migrate_copy(struct folio *newfolio, struct folio *folio);
>>> int folio_migrate_mapping(struct address_space *mapping,
>>> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
>>> index d356ab4047f7..d66556875d7d 100644
>>> --- a/include/linux/swapops.h
>>> +++ b/include/linux/swapops.h
>>> @@ -213,7 +213,7 @@ static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
>>> }
>>>
>>> extern void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
>>> - spinlock_t *ptl);
>>> + spinlock_t *ptl, bool unmap);
>>> extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
>>> unsigned long address);
>>> extern void migration_entry_wait_huge(struct vm_area_struct *vma,
>>> @@ -235,7 +235,7 @@ static inline int is_migration_entry(swp_entry_t swp)
>>> }
>>>
>>> static inline void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
>>> - spinlock_t *ptl) { }
>>> + spinlock_t *ptl, bool unmap) { }
>>> static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
>>> unsigned long address) { }
>>> static inline void migration_entry_wait_huge(struct vm_area_struct *vma,
>>> diff --git a/mm/filemap.c b/mm/filemap.c
>>> index 8f7e6088ee2a..18c353d52aae 100644
>>> --- a/mm/filemap.c
>>> +++ b/mm/filemap.c
>>> @@ -1389,6 +1389,7 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
>>> * @ptep: mapped pte pointer. Will return with the ptep unmapped. Only required
>>> * for pte entries, pass NULL for pmd entries.
>>> * @ptl: already locked ptl. This function will drop the lock.
>>> + * @unmap: indicating whether ptep need to be unmapped.
>>> *
>>> * Wait for a migration entry referencing the given page to be removed. This is
>>> * equivalent to put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE) except
>>> @@ -1402,7 +1403,7 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr,
>>> * there.
>>> */
>>> void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
>>> - spinlock_t *ptl)
>>> + spinlock_t *ptl, bool unmap)
>>> {
>>> struct wait_page_queue wait_page;
>>> wait_queue_entry_t *wait = &wait_page.wait;
>>> @@ -1439,10 +1440,9 @@ void migration_entry_wait_on_locked(swp_entry_t entry, pte_t *ptep,
>>> * a valid reference to the page, and it must take the ptl to remove the
>>> * migration entry. So the page is valid until the ptl is dropped.
>>> */
>>> - if (ptep)
>>> - pte_unmap_unlock(ptep, ptl);
>>> - else
>>> - spin_unlock(ptl);
>>> + spin_unlock(ptl);
>>> + if (unmap && ptep)
>>> + pte_unmap(ptep);
>>>
>>> for (;;) {
>>> unsigned int flags;
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 07668781c246..8088128c25db 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -6713,7 +6713,7 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
>>> } else {
>>> if (is_hugetlb_entry_migration(pte)) {
>>> spin_unlock(ptl);
>>> - __migration_entry_wait(mm, (pte_t *)pmd, ptl);
>>> + __migration_entry_wait(mm, (pte_t *)pmd, ptl, false);
>>> goto retry;
>>> }
>>> /*
>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>> index 98a968e6f465..5519261f54fe 100644
>>> --- a/mm/migrate.c
>>> +++ b/mm/migrate.c
>>> @@ -281,7 +281,7 @@ void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked)
>>> * When we return from this function the fault will be retried.
>>> */
>>> void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
>>> - spinlock_t *ptl)
>>> + spinlock_t *ptl, bool unmap)
>>> {
>>> pte_t pte;
>>> swp_entry_t entry;
>>> @@ -295,10 +295,12 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
>>> if (!is_migration_entry(entry))
>>> goto out;
>>>
>>> - migration_entry_wait_on_locked(entry, ptep, ptl);
>>> + migration_entry_wait_on_locked(entry, ptep, ptl, unmap);
>>> return;
>>> out:
>>> - pte_unmap_unlock(ptep, ptl);
>>> + spin_unlock(ptl);
>>> + if (unmap)
>>> + pte_unmap(ptep);
>>> }
>>>
>>> void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
>>> @@ -306,14 +308,14 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
>>> {
>>> spinlock_t *ptl = pte_lockptr(mm, pmd);
>>> pte_t *ptep = pte_offset_map(pmd, address);
>>> - __migration_entry_wait(mm, ptep, ptl);
>>> + __migration_entry_wait(mm, ptep, ptl, true);
>>> }
>>>
>>> void migration_entry_wait_huge(struct vm_area_struct *vma,
>>> struct mm_struct *mm, pte_t *pte)
>>> {
>>> spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
>>> - __migration_entry_wait(mm, pte, ptl);
>>> + __migration_entry_wait(mm, pte, ptl, false);
>>> }
>>>
>>> #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
>>> @@ -324,7 +326,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
>>> ptl = pmd_lock(mm, pmd);
>>> if (!is_pmd_migration_entry(*pmd))
>>> goto unlock;
>>> - migration_entry_wait_on_locked(pmd_to_swp_entry(*pmd), NULL, ptl);
>>> + migration_entry_wait_on_locked(pmd_to_swp_entry(*pmd), NULL, ptl, false);
>>> return;
>>> unlock:
>>> spin_unlock(ptl);
>> .
>>
