linux-kernel - Re: [PATCH 10/11] x86, rwsem: provide __down_write

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Message-ID: <5717EF59.1030709@zytor.com>
Date:	Wed, 20 Apr 2016 14:06:33 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Michal Hocko <mhocko@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"David S. Miller" <davem@...emloft.net>,
	Tony Luck <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Zankel <chris@...kel.net>,
	Max Filippov <jcmvbkbc@...il.com>, x86@...nel.org,
	linux-alpha@...r.kernel.org, linux-ia64@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
	linux-arch@...r.kernel.org, Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable

On 04/20/2016 01:45 PM, 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?
> 

Setting ret to sem doesn't make any sense.  Just use "=a" and "a".

	-hpa