[PATCH] arm64: spinlock: serialise spin_unlock_wait against concurrent lockers

[Boqun Feng]

Hi Will,

On Fri, Dec 11, 2015 at 09:46:52AM +0000, Will Deacon wrote:
> On Fri, Dec 11, 2015 at 04:09:11PM +0800, Boqun Feng wrote:
> > In conclusion, we have more than a half of uses working well already,
> > and each of the fix-needed ones has only one related critical section
> > and only one related data access in it. So on PPC, I think my proposal
> > won't have more smp_mb() instances to fix all current use cases than
> > adding smp_mb__after_unlock_lock() after the lock acquisition in each
> > related lock critical section.
> > 
> > Of course, my proposal needs the buy-ins of both PPC and ARM64v8, so
> > Paul and Will, what do you think? ;-)
> 
> I already queued the change promoting it to LOCK for arm64. It makes the
> semantics easy to understand and I've failed to measure any difference
> in performance. It's also robust against any future users of the macro
> and matches what other architectures do.
> 

Alright! I simply provided a candidate I came up with and relied on your
insight to pick a good one ;-)

Regards,
Boqun
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