RE: Fix unlock_buffer() to work the same way as bit_unlock()

From: Boehm, Hans <>
Date: 2006-03-31 09:17:28
[Trimmed linux-kernel, since this is IA64 specific.]
> From: Christoph Lameter 
> The question is what does fence imply for the order of the 
> atomic operation. Will the operation be performed before or 
> after the barrier? 
> Or do we need barriers on both sides?
I would assume so.

> If so then we may simulate that with a release and then do a 
> acquire load afterwards
> 	 cmpxchg_rel(m, old, new);
> 	 return *m;	/* m volatile so it has acquire semantics */

Is this really what you intended?

The cmpxchg and the read of *m are not atomic.  Operations in other
threads may intervene.

After looking at the spec again, I am convinced that it enforces
ordering.  But I'm not sure that helps.  I would guess that just adding
an mf at the end will give you at least similar performance.


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Received on Fri Mar 31 09:19:03 2006

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