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Message-Id: <20220804154050.e6ab9f8c38e2445acc5b57b1@linux-foundation.org>
Date: Thu, 4 Aug 2022 15:40:50 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Peter Xu <peterx@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Yang Shi <shy828301@...il.com>,
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, 3 Aug 2022 18:03:29 -0400 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().
Please (always) describe the user visible runtime effects of the bug
which is being fixed?
> --- 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
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