linux-kernel - Re: why are some atomic_t's not volatile, while most are?

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Message-Id: <20070808102705.9d91a14c.wjiang@resilience.com>
Date:	Wed, 8 Aug 2007 10:27:05 +0800
From:	Jerry Jiang <wjiang@...ilience.com>
To:	Chris Snook <csnook@...hat.com>
Cc:	Chris Friesen <cfriesen@...tel.com>,
	"Robert P. J. Day" <rpjday@...dspring.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: why are some atomic_t's not volatile, while most are?

On Tue, 07 Aug 2007 16:32:23 -0400
Chris Snook <csnook@...hat.com> wrote:

> > It seems like this would fall more into the case of the arch providing 
> > guarantees when using locked/atomic access rather than anything 
> > SMP-related, no?.
> 
> But if you're not using SMP, the only way you get a race condition is if your 
> compiler is reordering instructions that have side effects which are invisible 
> to the compiler.  This can happen with MMIO registers, but it's not an issue 
> with an atomic_t we're declaring in real memory.
> 

Under non-SMP, some compilers would reordering instructions as they think
and C standard informally guarantees all operations on volatile data
are executed in the sequence in which they appear in the source code,
right?

So no reordering happens with volatile, right?

-- Jerry

> 	-- Chris
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