linux-kernel - Re: [PATCH v3 4/4] mm/page_table_check: check entries at pmd levels

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Message-ID: <CA+CK2bCd6OXW+PEB6NYvAN61xaaPzT5dWr=REidWX1=e1jrNCg@mail.gmail.com>
Date:   Wed, 26 Jan 2022 07:46:09 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Turner <pjt@...gle.com>, Wei Xu <weixugc@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Muchun Song <songmuchun@...edance.com>,
        Fusion Future <qydwhotmail@...il.com>,
        Hugh Dickins <hughd@...gle.com>, Zi Yan <ziy@...dia.com>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v3 4/4] mm/page_table_check: check entries at pmd levels

On Wed, Jan 26, 2022 at 1:45 AM David Rientjes <rientjes@...gle.com> wrote:
>
> On Wed, 26 Jan 2022, Pasha Tatashin wrote:
>
> > syzbot detected a case where the page table counters were not properly
> > updated.
> >
>
> Is there a Reported-by tag that syzbot wants us to use to track this?

Google internal syzbot found it, so I did not add Reported-by as there
is no  public e-mail to reference. However, I added all the necessary
steps to repro this problem to the cover letter.

>
>
> This looks right, I'm wondering if we want to add a
> mmap_assert_write_locked(mm) to collapse_and_free_pmd().

Good idea, I will add it in the next revision.

Thanks,
Pasha