On Fri, Oct 12, 2018 at 06:31:58PM -0700, Joel Fernandes (Google) wrote:
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 9e68a02a52b1..2fd163cff406 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -191,6 +191,54 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
> drop_rmap_locks(vma);
> }
>
> +static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
> + unsigned long new_addr, unsigned long old_end,
> + pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush)
> +{
> + spinlock_t *old_ptl, *new_ptl;
> + struct mm_struct *mm = vma->vm_mm;
> +
> + if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK)
> + || old_end - old_addr < PMD_SIZE)
> + return false;
> +
> + /*
> + * The destination pmd shouldn't be established, free_pgtables()
> + * should have release it.
> + */
> + if (WARN_ON(!pmd_none(*new_pmd)))
> + return false;
> +
> + /*
> + * We don't have to worry about the ordering of src and dst
> + * ptlocks because exclusive mmap_sem prevents deadlock.
> + */
> + old_ptl = pmd_lock(vma->vm_mm, old_pmd);
> + if (old_ptl) {
How can it ever be false?
> + pmd_t pmd;
> +
> + new_ptl = pmd_lockptr(mm, new_pmd);
> + if (new_ptl != old_ptl)
> + spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
> +
> + /* Clear the pmd */
> + pmd = *old_pmd;
> + pmd_clear(old_pmd);
> +
> + VM_BUG_ON(!pmd_none(*new_pmd));
> +
> + /* Set the new pmd */
> + set_pmd_at(mm, new_addr, new_pmd, pmd);
> + if (new_ptl != old_ptl)
> + spin_unlock(new_ptl);
> + spin_unlock(old_ptl);
> +
> + *need_flush = true;
> + return true;
> + }
> + return false;
> +}
> +
--
Kirill A. Shutemov
