RFR(S) 8067331: Zero: Atomic::xchg and Atomic::xchg_ptr need full memory barrier

[Severin Gehwolf]

On Wed, 2015-01-07 at 15:07 +1000, David Holmes wrote:
> Severin,
> 
> Can you create a changeset with myself (dholmes) and Coleen (coleenp) as 
> Reviewers, and with the file copyrights suitably updated. I'm not sure 
> what form that will take given the dual copyright attributions but 
> presumably the Red Hat line will need 2015 added.
> 
> If you email me the changeset directly I will apply it to the 
> jdk9/hs-rt/hotspot/ forest.

I've sent the exported changeset to you privately, David. Thanks for the
reviews, David and Coleen!

Cheers,
Severin

> Thanks,
> David
> 
> On 7/01/2015 2:59 PM, David Holmes wrote:
> > On 7/01/2015 2:54 PM, Coleen Phillimore wrote:
> >>
> >> This looks good.  Sorry for the delay reviewing it as it looks
> >> important.  Is there a small test case that can be written to test
> >> this?  (or no?)
> >
> > No - I'll add noreg-hard. Testing for a missing memory-barrier is not
> > practical.
> >
> > Thanks,
> > David
> >
> >> Coleen
> >>
> >> On 1/6/15, 8:47 PM, David Holmes wrote:
> >>> Can we get a second hotspot review please - this is quite straight
> >>> forward.
> >>>
> >>> Thanks,
> >>> David
> >>>
> >>> On 5/01/2015 12:21 PM, David Holmes wrote:
> >>>> Hi Severin,
> >>>>
> >>>> Sorry this slipped through the cracks before the holidays.
> >>>>
> >>>> On 16/12/2014 1:09 AM, Severin Gehwolf wrote:
> >>>>> Hi,
> >>>>>
> >>>>> Could someone please review and sponsor the following change?
> >>>>>
> >>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8067331
> >>>>> webrev:
> >>>>> http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8067331/webrev.02/
> >>>>>
> >>>>> The issue is that all atomic operations are expected to be full memory
> >>>>> barriers, but two implementations of the Zero variant JVM -
> >>>>> Atomic::xchg
> >>>>> and Atomic::xchg_ptr - use GCC's built-in __sync_lock_test_and_set
> >>>>> which
> >>>>> is an acquire barrier only. The fix adds full memory barriers manually
> >>>>> for those.
> >>>>>
> >>>>> Thoughts?
> >>>>
> >>>> Looks completely consistent with what I just saw in the aarch64 port
> >>>> code.
> >>>>
> >>>> I can sponsor this but we still need a second review.
> >>>>
> >>>> Thanks,
> >>>> David
> >>>>
> >>>>> Cheers,
> >>>>> Severin
> >>>>>
> >>