linux-kernel - Re: [PATCH] mm/debug_vm_pgtable: clear page table entries at destroy

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Message-Id: <20250814162801.08ece6844de66ac43af5224f@linux-foundation.org>
Date: Thu, 14 Aug 2025 16:28:01 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: "Herton R. Krzesinski" <herton@...hat.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/debug_vm_pgtable: clear page table entries at
 destroy_args()

On Thu, 14 Aug 2025 16:16:03 +0530 Anshuman Khandual <anshuman.khandual@....com> wrote:

> On 01/08/25 3:10 AM, Herton R. Krzesinski wrote:
> > The mm/debug_vm_pagetable test allocates manually page table entries for the
> > tests it runs, using also its manually allocated mm_struct. That in itself is
> > ok, but when it exits, at destroy_args() it fails to clear those entries with
> > the *_clear functions.
> > 
> > The problem is that leaves stale entries. If another process allocates
> > an mm_struct with a pgd at the same address, it may end up running into
> > the stale entry. This is happening in practice on a debug kernel with
> > CONFIG_DEBUG_VM_PGTABLE=y, for example this is the output with some
> > extra debugging I added (it prints a warning trace if pgtables_bytes goes
> > negative, in addition to the warning at check_mm() function):
>
> This has been on linux-next for almost last two weeks now and
> no problem has been reported. So I guess it's all good.
> 

[top-posting repaired]

Thanks, I'll move this into the next batch for sending into mainline.