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

Boqun Feng
2015-11-12T14:49:33Z

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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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