Re: [PATCH 4/4] locking: Introduce smp_cond_acquire()

[Boqun Feng]

On Thu, Nov 12, 2015 at 06:40:04AM -0800, Paul E. McKenney wrote:
[snip]
> 
> I cannot resist suggesting that any lock that interacts with
> spin_unlock_wait() must have all relevant acquisitions followed by
> smp_mb__after_unlock_lock().
> 

But

1.      This would expand the purpose of smp_mb__after_unlock_lock(),
        right? smp_mb__after_unlock_lock() is for making UNLOCK-LOCK
        pair global transitive rather than guaranteeing no operations
        can be reorder before the STORE part of LOCK/ACQUIRE.

2.      If ARM64 has the same problem as PPC now,
        smp_mb__after_unlock_lock() can't help, as it's a no-op on
        ARM64.

Regards,
Boqun

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