linux-kernel - Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

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Message-ID: <CAHbLzkoztB1LNOtNWa=8GPABF5xConGox2D1ebdD97467Ykb1A@mail.gmail.com>
Date:   Thu, 4 Aug 2022 10:43:47 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nadav Amit <nadav.amit@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Konstantin Khlebnikov <khlebnikov@...nvz.org>
Subject: Re: [PATCH] mm/smaps: Don't access young/dirty bit if pte unpresent

On Wed, Aug 3, 2022 at 3:03 PM Peter Xu <peterx@...hat.com> wrote:
>
> These bits should only be valid when the ptes are present.  Introducing two
> booleans for it and set it to false when !pte_present().
>
> Cc: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries", 2012-05-31)
> Signed-off-by: Peter Xu <peterx@...hat.com>

Reviewed-by: Yang Shi <shy828301@...il.com>

> ---
>  fs/proc/task_mmu.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 9913f3be9fd2..482f91577f8c 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -527,10 +527,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
>         struct vm_area_struct *vma = walk->vma;
>         bool locked = !!(vma->vm_flags & VM_LOCKED);
>         struct page *page = NULL;
> -       bool migration = false;
> +       bool migration = false, young = false, dirty = false;
>
>         if (pte_present(*pte)) {
>                 page = vm_normal_page(vma, addr, *pte);
> +               young = pte_young(*pte);
> +               dirty = pte_dirty(*pte);
>         } else if (is_swap_pte(*pte)) {
>                 swp_entry_t swpent = pte_to_swp_entry(*pte);
>
> @@ -560,8 +562,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
>         if (!page)
>                 return;
>
> -       smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
> -                     locked, migration);
> +       smaps_account(mss, page, false, young, dirty, locked, migration);
>  }
>
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> --
> 2.32.0
>