linux-kernel - Re: [PATCH 08/31] kasan, page_alloc: refactor init checks in post_alloc

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Date:   Thu, 2 Dec 2021 17:13:34 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Marco Elver <elver@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Evgenii Stepanov <eugenis@...gle.com>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH 08/31] kasan, page_alloc: refactor init checks in post_alloc_hook

On Tue, Nov 30, 2021 at 10:41 PM <andrey.konovalov@...ux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@...gle.com>
>
> This patch separates code for zeroing memory from the code clearing tags
> in post_alloc_hook().
>
> This patch is not useful by itself but makes the simplifications in
> the following patches easier to follow.
>
> This patch does no functional changes.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  mm/page_alloc.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2ada09a58e4b..0561cdafce36 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2406,19 +2406,21 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
>                 kasan_alloc_pages(page, order, gfp_flags);
>         } else {
>                 bool init = !want_init_on_free() && want_init_on_alloc(gfp_flags);
> +               bool init_tags = init && (gfp_flags & __GFP_ZEROTAGS);
>
>                 kasan_unpoison_pages(page, order, init);
>
> -               if (init) {
> -                       if (gfp_flags & __GFP_ZEROTAGS) {
> -                               int i;
> +               if (init_tags) {
> +                       int i;
>
> -                               for (i = 0; i < 1 << order; i++)
> -                                       tag_clear_highpage(page + i);
> -                       } else {
> -                               kernel_init_free_pages(page, 1 << order);
> -                       }
> +                       for (i = 0; i < 1 << order; i++)
> +                               tag_clear_highpage(page + i);
> +
> +                       init = false;

I find this a bit twisted and prone to breakages.
Maybe just check for (init && !init_tags) below?
>                 }
> +
> +               if (init)
> +                       kernel_init_free_pages(page, 1 << order);
>         }
>
>         set_page_owner(page, order, gfp_flags);
> --
> 2.25.1
>


-- 
Alexander Potapenko
Software Engineer

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