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Re: [PULL 13/14] virtio-ccw: fix virtio_set_ind_atomic

From: Halil Pasic
Subject: Re: [PULL 13/14] virtio-ccw: fix virtio_set_ind_atomic
Date: Tue, 8 Sep 2020 11:34:28 +0200

On Fri,  3 Jul 2020 12:06:49 +0200
Cornelia Huck <cohuck@redhat.com> wrote:

> From: Halil Pasic <pasic@linux.ibm.com>
> The atomic_cmpxchg() loop is broken because we occasionally end up with
> old and _old having different values (a legit compiler can generate code
> that accessed *ind_addr again to pick up a value for _old instead of
> using the value of old that was already fetched according to the
> rules of the abstract machine). This means the underlying CS instruction
> may use a different old (_old) than the one we intended to use if
> atomic_cmpxchg() performed the xchg part.


I believe this fix should be considered for stable. Unfortunately we
didn't think about it back then.


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