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Date: Wed, 11 Aug 2010 16:41:52 +1000
From: Paul Mackerras <paulus@samba.org>
To: Anton Blanchard <anton@samba.org>
Subject: Re: [PATCH] powerpc: Feature nop out reservation clear when stcx
	checks address
Message-ID: <20100811064152.GC15252@drongo>
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On Wed, Aug 11, 2010 at 03:20:05PM +1000, Anton Blanchard wrote:

> All recent POWER CPUs check the address before letting the stcx succeed
> so we can create a CPU feature and nop it out. As Ben suggested, we can
> only do this in our syscall path because there is a remote possibility
> some kernel code gets interrupted by an exception that ends up operating
> on the same cacheline.

Nice...  Just one nit, and that is that I think we now need a dummy
stcx in the context switch code so there is no possibility of getting
from one user context to another with a reservation still pending from
the first context.  I guess our chances of getting through schedule()
without doing any atomics, bitops or spinlocks are pretty remote, but
nevertheless it might be as well to make sure.

Paul.