linux-kernel - Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

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Message-ID: <20070815081841.GA16551@osiris.boeblingen.de.ibm.com>
Date:	Wed, 15 Aug 2007 10:18:41 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Chris Snook <csnook@...hat.com>, satyam@...radead.org,
	clameter@....com, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, torvalds@...ux-foundation.org,
	netdev@...r.kernel.org, akpm@...ux-foundation.org, ak@...e.de,
	davem@...emloft.net, schwidefsky@...ibm.com, wensong@...ux-vs.org,
	horms@...ge.net.au, wjiang@...ilience.com, cfriesen@...tel.com,
	zlynx@....org, rpjday@...dspring.com, jesper.juhl@...il.com,
	segher@...nel.crashing.org
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
	architectures

On Wed, Aug 15, 2007 at 02:49:03PM +0800, Herbert Xu wrote:
> Chris Snook <csnook@...hat.com> wrote:
> > 
> > Because atomic operations are generally used for synchronization, which requires 
> > volatile behavior.  Most such codepaths currently use an inefficient barrier(). 
> >  Some forget to and we get bugs, because people assume that atomic_read() 
> > actually reads something, and atomic_write() actually writes something.  Worse, 
> > these are architecture-specific, even compiler version-specific bugs that are 
> > often difficult to track down.
> 
> I'm yet to see a single example from the current tree where
> this patch series is the correct solution.  So far the only
> example has been a buggy piece of code which has since been
> fixed with a cpu_relax.

Btw.: we still have

include/asm-i386/mach-es7000/mach_wakecpu.h:  while (!atomic_read(deassert));
include/asm-i386/mach-default/mach_wakecpu.h: while (!atomic_read(deassert));

Looks like they need to be fixed as well.
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