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Date: Wed, 20 Apr 2016 16:58:26 -0400
From: Michal Hocko <mhocko@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Peter Zijlstra <peterz@infradead.org>,
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        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable
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On Wed 20-04-16 22:45:01, Borislav Petkov wrote:
> On Wed, Apr 20, 2016 at 11:04:05AM -0700, H. Peter Anvin wrote:
> > The reason it breaks is because the same register can't be an
> > input-output register and a separate input. However, the input side of
> > the input-output is probably undefined, and so gcc may not notice.
> 
> So Michal and I talked about this a while ago. Why do we need the '"a"
> (sem)' input dependency if '"+a" (ret)' already supplies the same thing?
> 
> There's also that "=d" (tmp) thing which we don't really need as an
> output, right?
> 
> I.e., can we simplify like this?

I am for any simplification, my gcc-asm-foo is just too weak and I
wanted my change to be as minimal as possible. So if you feel you can
clean up this I would more than welcome that. Maybe a follow up patch
would be a better approach so that we can check that the generated code
hasn't changed.

Thanks!
-- 
Michal Hocko
SUSE Labs