Re: [PATCH v4 2/9] mm: pagewalk: Take the pagetable lock in walk_pte_range()

[Linus Torvalds]

On Wed, Oct 9, 2019 at 8:14 AM Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
>
> If ->pte_entry() fails on the first entry of the page table, pte - 1 will
> point out side the page table.
>
> And the '- 1' is totally unnecessary as we break the loop before pte++ on
> the last iteration.

Good catch. Too much copying the wrong pattern from other sources.

I do wish we didn't have this pattern of "update pte, then do
pte_unmap as long as it's in the same page". Yeah, it avoids a
variable, but still... But it is what it is, and we just need to be
careful.

             Linus