Hello,
On Thu, Jun 15, 2017 at 05:52:24PM +0300, Kirill A. Shutemov wrote:
> This patch uses modifed pmdp_invalidate(), that return previous value of pmd,
> to transfer dirty and accessed bits.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> fs/proc/task_mmu.c | 8 ++++----
> mm/huge_memory.c | 29 ++++++++++++-----------------
> 2 files changed, 16 insertions(+), 21 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index f0c8b33d99b1..f2fc1ef5bba2 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -906,13 +906,13 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
> static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,
> unsigned long addr, pmd_t *pmdp)
> {
> - pmd_t pmd = *pmdp;
> + pmd_t old, pmd = *pmdp;
>
> /* See comment in change_huge_pmd() */
> - pmdp_invalidate(vma, addr, pmdp);
> - if (pmd_dirty(*pmdp))
> + old = pmdp_invalidate(vma, addr, pmdp);
> + if (pmd_dirty(old))
> pmd = pmd_mkdirty(pmd);
> - if (pmd_young(*pmdp))
> + if (pmd_young(old))
> pmd = pmd_mkyoung(pmd);
>
> pmd = pmd_wrprotect(pmd);
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index a84909cf20d3..0433e73531bf 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1777,17 +1777,7 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> * pmdp_invalidate() is required to make sure we don't miss
> * dirty/young flags set by hardware.
> */
> - entry = *pmd;
> - pmdp_invalidate(vma, addr, pmd);
> -
> - /*
> - * Recover dirty/young flags. It relies on pmdp_invalidate to not
> - * corrupt them.
> - */
> - if (pmd_dirty(*pmd))
> - entry = pmd_mkdirty(entry);
> - if (pmd_young(*pmd))
> - entry = pmd_mkyoung(entry);
> + entry = pmdp_invalidate(vma, addr, pmd);
>
> entry = pmd_modify(entry, newprot);
> if (preserve_write)
> @@ -1927,8 +1917,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> struct mm_struct *mm = vma->vm_mm;
> struct page *page;
> pgtable_t pgtable;
> - pmd_t _pmd;
> - bool young, write, dirty, soft_dirty;
> + pmd_t old, _pmd;
> + bool young, write, soft_dirty;
> unsigned long addr;
> int i;
>
> @@ -1965,7 +1955,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> page_ref_add(page, HPAGE_PMD_NR - 1);
> write = pmd_write(*pmd);
> young = pmd_young(*pmd);
> - dirty = pmd_dirty(*pmd);
> soft_dirty = pmd_soft_dirty(*pmd);
>
> pmdp_huge_split_prepare(vma, haddr, pmd);
> @@ -1995,8 +1984,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> if (soft_dirty)
> entry = pte_mksoft_dirty(entry);
> }
> - if (dirty)
> - SetPageDirty(page + i);
> pte = pte_offset_map(&_pmd, addr);
> BUG_ON(!pte_none(*pte));
> set_pte_at(mm, addr, pte, entry);
> @@ -2045,7 +2032,15 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> * and finally we write the non-huge version of the pmd entry with
> * pmd_populate.
> */
> - pmdp_invalidate(vma, haddr, pmd);
> + old = pmdp_invalidate(vma, haddr, pmd);
> +
> + /*
> + * Transfer dirty bit using value returned by pmd_invalidate() to be
> + * sure we don't race with CPU that can set the bit under us.
> + */
> + if (pmd_dirty(old))
> + SetPageDirty(page);
> +
When I see this, without this patch, MADV_FREE has been broken because
it can lose dirty bit by early checking. Right?
If so, isn't it a candidate for -stable?
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