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Date: Tue, 8 Mar 2022 20:19:58 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: "Huang, Ying" <ying.huang@...el.com>
CC: <akpm@...ux-foundation.org>, <mike.kravetz@...cle.com>,
<shy828301@...il.com>, <willy@...radead.org>, <ziy@...dia.com>,
<minchan@...nel.org>, <apopple@...dia.com>,
<ave.hansen@...ux.intel.com>, <o451686892@...il.com>,
<almasrymina@...gle.com>, <jhubbard@...dia.com>,
<rcampbell@...dia.com>, <peterx@...hat.com>,
<naoya.horiguchi@....com>, <mhocko@...e.com>, <riel@...hat.com>,
<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 16/16] mm/migration: fix potential pte_unmap on an not
mapped pte
On 2022/3/7 13:37, Huang, Ying wrote:
> Miaohe Lin <linmiaohe@...wei.com> 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). So I can't paste the err log. And The
issues from this series mainly come from the code investigating with some tests.
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@...wei.com>
>> ---
>> 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);
> .
>
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