linux-kernel - Re: [PATCH] make atomic_t volatile on all architectures

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Message-ID: <20070809081419.GA9580@osiris.boeblingen.de.ibm.com>
Date:	Thu, 9 Aug 2007 10:14:19 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Chris Snook <csnook@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org, ak@...e.de, davem@...emloft.net,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au,
	wjiang@...ilience.com, cfriesen@...tel.com, zlynx@....org
Subject: Re: [PATCH] make atomic_t volatile on all architectures

On Thu, Aug 09, 2007 at 03:31:10AM -0400, Chris Snook wrote:
>  Linus Torvalds wrote:
> > I'd be *much* happier with "atomic_read()" doing the "volatile" instead.
> > The fact is, volatile on data structures is a bug. It's a wart in the C 
> > language. It shouldn't be used. Volatile accesses in *code* can be ok, and 
> > if we have "atomic_read()" expand to a "*(volatile int *)&(x)->value", then 
> > I'd be ok with that.
> > But marking data structures volatile just makes the compiler screw up 
> > totally, and makes code for initialization sequences etc much worse.
> > 		Linus
> 
>  Fair enough.  Casting to (volatile int *) will give us the behavior people 
>  expect when using atomic_t without needing to use inefficient barriers.
> 
>  While we have the hood up, should we convert all the atomic_t's to 
>  non-volatile and put volatile casts in all the atomic_reads?  I don't know 
>  enough about the various arches to say with confidence that those changes 
>  alone will preserve existing behavior.  We might need some arch-specific 
>  tweaking of the atomic operations.

If you write that patch could you include the atomic64 variants as well,
please? Besides that just post the patch to linux-arch and maintainers
should speak up.
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