Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220901173516.702122-1-surenb@google.com> <20220901173516.702122-9-surenb@google.com>
 <dcefc6dd-f8eb-945e-37ab-3c0c4e4e20f2@linux.ibm.com>
In-Reply-To: <dcefc6dd-f8eb-945e-37ab-3c0c4e4e20f2@linux.ibm.com>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Thu, 8 Sep 2022 17:15:31 -0700
Message-ID: <CAJuCfpHSVS1O=V5+gjm8bboG0FJzZtxo1UYrjoU0+r57o-4zYg@mail.gmail.com>
Subject: Re: [RFC PATCH RESEND 08/28] mm/khugepaged: mark VMA as locked while
 collapsing a hugepage
To:     Laurent Dufour <ldufour@linux.ibm.com>
Cc:     akpm@linux-foundation.org, michel@lespinasse.org,
        jglisse@google.com, mhocko@suse.com, vbabka@suse.cz,
        hannes@cmpxchg.org, mgorman@suse.de, dave@stgolabs.net,
        willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org,
        laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org,
        songliubraving@fb.com, peterx@redhat.com, david@redhat.com,
        dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de,
        kent.overstreet@linux.dev, rientjes@google.com,
        axelrasmussen@google.com, joelaf@google.com, minchan@google.com,
        kernel-team@android.com, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, Sep 6, 2022 at 7:43 AM Laurent Dufour <ldufour@linux.ibm.com> wrote=
:
>
> Le 01/09/2022 =C3=A0 19:34, Suren Baghdasaryan a =C3=A9crit :
> > Protect VMA from concurrent page fault handler while modifying it in
> > collapse_huge_page.
>
> Is the goal to protect changes in the anon_vma structure?
>
> AFAICS, the vma it self is not impacted here, only the anon_vma and the
> PMD/PTE are touched, and they have their own protection mechanism, isn't =
it?

Yes, I think you are right about not needing to lock VMA here as all
modified components are already protected. Thanks!

>
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> >  mm/khugepaged.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index 01f71786d530..030680633989 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -1072,6 +1072,7 @@ static void collapse_huge_page(struct mm_struct *=
mm,
> >       if (mm_find_pmd(mm, address) !=3D pmd)
> >               goto out_up_write;
> >
> > +     vma_mark_locked(vma);
> >       anon_vma_lock_write(vma->anon_vma);
> >
> >       mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
>