netdev - Re: [PATCH 0/3] virtio/vringh: kill off ACCESS

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Message-ID: <20161125180649.GC30811@leverpostej>
Date:   Fri, 25 Nov 2016 18:07:03 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Davidlohr Bueso <dbueso@...e.de>,
        Jason Wang <jasowang@...hat.com>,
        KVM list <kvm@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE()

On Fri, Nov 25, 2016 at 09:52:50AM -0800, Linus Torvalds wrote:
> READ/WRITE_ONCE() are atomic *WHEN*THAT*IS*POSSIBLE*.

> But sometimes it's not going to be atomic.

That's the problem.

Common code may rely on something being atomic when that's only true on
a subset of platforms. On others, it's silently "fixed" into something
that isn't atomic, and we get no diagnostic. The bug lurks beneath the
surface.

Thanks,
Mark.