linux-kernel - Re: [PATCH v3 1/7] kernel/fork: convert vma assignment to a memcpy

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Date:   Wed, 25 Jan 2023 17:34:49 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...hsingularity.net,
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        peterz@...radead.org, ldufour@...ux.ibm.com, paulmck@...nel.org,
        mingo@...hat.com, will@...nel.org, luto@...nel.org,
        songliubraving@...com, peterx@...hat.com, david@...hat.com,
        dhowells@...hat.com, hughd@...gle.com, bigeasy@...utronix.de,
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        leewalsh@...gle.com, posk@...gle.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v3 1/7] kernel/fork: convert vma assignment to a memcpy

On Wed, 25 Jan 2023 16:50:01 -0800 Suren Baghdasaryan <surenb@...gle.com> wrote:

> On Wed, Jan 25, 2023 at 4:22 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Wed, 25 Jan 2023 15:35:48 -0800 Suren Baghdasaryan <surenb@...gle.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.