Re: [PATCH 0/2] two atomic_cmpxchg() related fixes

[Halil Pasic <pasic@linux.ibm.com>]

On Wed, 1 Jul 2020 14:06:11 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> 
> 
> On 01.07.20 14:01, Cornelia Huck wrote:
> > On Tue, 16 Jun 2020 06:50:33 +0200
> > Halil Pasic <pasic@linux.ibm.com> wrote:
> > 
> >> The story short: compiler can generate code that does two
> >> distinct fetches of *ind_addr for old and _old. If that happens we can
> >> not figure out if we had the desired xchg or not.
> >>
> >> Halil Pasic (2):
> >>   virtio-ccw: fix virtio_set_ind_atomic
> >>   s390x/pci: fix set_ind_atomic
> >>
> >>  hw/s390x/s390-pci-bus.c | 16 +++++++++-------
> >>  hw/s390x/virtio-ccw.c   | 18 ++++++++++--------
> >>  2 files changed, 19 insertions(+), 15 deletions(-)
> >>
> >>
> >> base-commit: 7d3660e79830a069f1848bb4fa1cdf8f666424fb
> > 
> > Have we managed to reach any kind of agreement on this? (A v2?)
> > 
> > We can still get in fixes post-softfreeze, of course.
> 
> Unless Halil has a v2 ready, 
> I think the current patch is fine as is as a fix. I would suggest
> to go with that and we can then do more beautification later when
> necessary.
> 
> 

I think we were waiting for Paolo to chime in regarding the barrier().
The thing I could beautify is using atomic_read(), but frankly I'm not
sure about it, especially considering multi-proccess. My understanding of
volatile is better than my understanding of atomic_read(). On the other
hand, same multi-process question can be asked about atomic_cmpxchg()
and __atomic_compare_exchange_n()...

Regards,
Halil