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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 9 Oct 2019 09:07:00 -0700
Message-ID: <CAHk-=wh=zsXPmSTJJgEgVr4ebgwTQ-wx-P1c7+koJAK-h2f_vQ@mail.gmail.com>
Subject: Re: [PATCH v4 2/9] mm: pagewalk: Take the pagetable lock in walk_pte_range()
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
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        Will Deacon <will.deacon@arm.com>,
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        Rik van Riel <riel@surriel.com>,
        Minchan Kim <minchan@kernel.org>,
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On Wed, Oct 9, 2019 at 8:14 AM Kirill A. Shutemov <kirill@shutemov.name> 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