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Date: Tue, 7 Mar 2006 10:40:57 -0700
From: Matthew Wilcox <matthew@wil.cx>
Subject: Re: Memory barriers and spin_unlock safety
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To: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@osdl.org>, akpm@osdl.org, ak@suse.de, mingo@redhat.com, jblunck@suse.de, bcrl@linux.intel.com, linux-arch@vger.kernel.org, linuxppc64-dev@ozlabs.org, linux-kernel@vger.kernel.org
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On Tue, Mar 07, 2006 at 05:36:59PM +0000, David Howells wrote:
> David Howells <dhowells@redhat.com> wrote:
> 
> > I suspect, then, that x86_64 should not have an SFENCE for smp_wmb(), and
> > that only io_wmb() should have that.
> 
> Hmmm... We don't actually have io_wmb()... Should the following be added to
> all archs?
> 
> 	io_mb()
> 	io_rmb()
> 	io_wmb()

it's spelled mmiowb(), and reads from IO space are synchronous, so don't
need barriers.