linux-kernel - Re: [PATCH] futex: cmpxchg_futex_value

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Message-ID: <20110307095438.7d963d0f@mschwide.boeblingen.de.ibm.com>
Date:	Mon, 7 Mar 2011 09:54:38 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Darren Hart <dvhltc@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Matt Turner <mattst88@...il.com>,
	Russell King <linux@....linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Michal Simek <monstr@...str.eu>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Metcalf <cmetcalf@...era.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] futex: cmpxchg_futex_value_locked API change

On Sun, 6 Mar 2011 18:11:27 -0800
Michel Lespinasse <walken@...gle.com> wrote:

> Aplogies for the long CC list - as this proposal involves asm changes
> in many architectures, and I have only been able to test on x86,
> I have tried to include one maintainer from every arch so they can
> hopefully double check me. I do think I got all architectures right,
> but you can never be 100% sure...
> 
> -static int __futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
> +static int __futex_atomic_cmpxchg_pt(int *uval, int __user *uaddr,
> +				     int oldval, int newval)
>  {
>  	int ret;
> 
>  	asm volatile("0: cs   %1,%4,0(%5)\n"
> -		     "1: lr   %0,%1\n"
> +		     "1: l    %0,0\n"
>  		     "2:\n"
>  		     EX_TABLE(0b,2b) EX_TABLE(1b,2b)
>  		     : "=d" (ret), "+d" (oldval), "=m" (*uaddr)
>  		     : "0" (-EFAULT), "d" (newval), "a" (uaddr), "m" (*uaddr)
>  		     : "cc", "memory" );
> +	*uval = oldval;
>  	return ret;
>  }

That "l %0,0" is incorrect; if you want to load a zero into %0 you can use "la %0,0".

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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