Date:   Wed, 25 Jan 2023 17:34:49 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
        vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net,
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        mingo@redhat.com, will@kernel.org, luto@kernel.org,
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        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com,
        "Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH v3 1/7] kernel/fork: convert vma assignment to a memcpy
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On Wed, 25 Jan 2023 16:50:01 -0800 Suren Baghdasaryan <surenb@google.com> wrote:

> On Wed, Jan 25, 2023 at 4:22 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Wed, 25 Jan 2023 15:35:48 -0800 Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > > Convert vma assignment in vm_area_dup() to a memcpy() to prevent compiler
> > > errors when we add a const modifier to vma->vm_flags.
> > >
> > > ...
> > >
> > > --- a/kernel/fork.c
> > > +++ b/kernel/fork.c
> > > @@ -482,7 +482,7 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
> > >                * orig->shared.rb may be modified concurrently, but the clone
> > >                * will be reinitialized.
> > >                */
> > > -             *new = data_race(*orig);
> > > +             memcpy(new, orig, sizeof(*new));
> >
> > The data_race() removal is unchangelogged?
> 
> True. I'll add a note in the changelog about that. Ideally I would
> like to preserve it but I could not find a way to do that.
> 

Perhaps Paul can comment?

I wonder if KCSAN knows how to detect this race, given that it's now in
a memcpy.  I assume so.