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

[will.deacon@arm.com (Will Deacon)]

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.

Will