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From: Cornelia Huck <cohuck@redhat.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>,
	Matthew Rosato <mjrosato@linux.ibm.com>,
	David Hildenbrand <david@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	qemu-devel@nongnu.org,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	qemu-s390x@nongnu.org, Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH 0/2] two atomic_cmpxchg() related fixes
Date: Fri, 3 Jul 2020 16:03:32 +0200
Message-ID: <20200703160332.78301244.cohuck@redhat.com> (raw)
In-Reply-To: <20200703153711.3aa18ac7.pasic@linux.ibm.com>

On Fri, 3 Jul 2020 15:37:11 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> 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()...

We can just improve the code on top later. Having something that
works now beats something not yet developed that might be nicer :)

(But yes, it also might be good to look at non-s390 examples of this
pattern and check if something can be done in a more central place.)



  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-16  4:50 Halil Pasic
2020-06-16  4:50 ` [PATCH 1/2] virtio-ccw: fix virtio_set_ind_atomic Halil Pasic
2020-06-16  5:58   ` Christian Borntraeger
2020-06-16  6:33     ` Cornelia Huck
2020-06-16  6:45       ` Christian Borntraeger
2020-06-19  7:14         ` Cornelia Huck
2020-06-17 23:56       ` Halil Pasic
2020-06-19  7:33         ` David Hildenbrand
2020-06-19  8:17           ` Halil Pasic
2020-06-16  9:31     ` Halil Pasic
2020-07-01 13:13   ` Christian Borntraeger
2020-07-04 18:34   ` Michael S. Tsirkin
2020-07-06  5:44     ` Christian Borntraeger
2020-07-06 11:19     ` Halil Pasic
2020-06-16  4:50 ` [PATCH 2/2] s390x/pci: fix set_ind_atomic Halil Pasic
2020-07-01 13:14   ` Christian Borntraeger
2020-07-01 12:01 ` [PATCH 0/2] two atomic_cmpxchg() related fixes Cornelia Huck
2020-07-01 12:06   ` Christian Borntraeger
2020-07-01 13:10     ` Cornelia Huck
2020-07-03 13:37     ` Halil Pasic
2020-07-03 14:03       ` Cornelia Huck [this message]
2020-07-02 11:18 ` Cornelia Huck

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