From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE()
Date: Fri, 25 Nov 2016 18:07:03 +0000
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Cc: Dmitry Vyukov <dvyukov@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Davidlohr Bueso <dbueso@suse.de>,
        Jason Wang <jasowang@redhat.com>,
        KVM list <kvm@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        virtualization <virtualization@lists.linux-foundation.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
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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.