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Subject: Re: [PATCH 0/2] fix vma->anon_vma check for per-VMA locking; fix
 anon_vma memory ordering
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <CAHk-=wgeMOvL=ko_eruf5St7h0e9dVn4+GMKjcdshTJoxyD8tw@mail.gmail.com>
Date:   Thu, 27 Jul 2023 13:11:43 -0700
Cc:     Will Deacon <will@kernel.org>, Jann Horn <jannh@google.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        Akira Yokosawa <akiyks@gmail.com>,
        Daniel Lustig <dlustig@nvidia.com>,
        Joel Fernandes <joel@joelfernandes.org>
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To:     Linus Torvalds <torvalds@linuxfoundation.org>
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> On Jul 27, 2023, at 12:39 PM, Linus Torvalds =
<torvalds@linuxfoundation.org> wrote:
>=20
> On Thu, 27 Jul 2023 at 12:10, Nadav Amit <nadav.amit@gmail.com> wrote:
>>=20
>> Interesting. I wonder if you considered adding to READ_ONCE() =
something
>> like:
>>=20
>>        asm volatile("" : "+g" (x) );
>>=20
>> So later loads (such as baz =3D *ptr) would reload the updated value.
>=20
> Not necessarily a bad idea.  Although I suspect you'd want to add
> *two* of them - on either side - to make sure any previous loads
> wouldn't be moved around it either.

You are right, two are needed.

I=E2=80=99ll give it a shot and see if I see changes to the binary.