linux-kernel - Re: x86-32: clean up rwsem inline asm statements

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Message-ID: <alpine.LFD.2.00.1001121725110.17145@localhost.localdomain>
Date:	Tue, 12 Jan 2010 17:26:47 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andreas Schwab <schwab@...ux-m68k.org>
cc:	Ingo Molnar <mingo@...e.hu>, Peter Anvin <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: x86-32: clean up rwsem inline asm statements



On Wed, 13 Jan 2010, Andreas Schwab wrote:

> Linus Torvalds <torvalds@...ux-foundation.org> writes:
> 
> > @@ -249,7 +249,7 @@ static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
> >  {
> >  	int tmp = delta;
> >  
> > -	asm volatile(LOCK_PREFIX "xadd %0,%1"
> > +	asm volatile(LOCK_PREFIX "xadd%z0 %0,%1"
> >  		     : "+r" (tmp), "+m" (sem->count)
> >  		     : : "memory");
> 
> I think %z0 should be %z1 here.

You're right, but Peter made it all a non-issue anyway.

Thanks for noticing, though, since it implies that somebody read the patch 
carefully. It's always a bit scary to change fundamental inline asms, 
especially for something like a locking routine where the core _semantics_ 
are so subtle (and if you get locking wrong, things may still work - you 
just end up with some really odd race conditions).

		Linus
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