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Date:	Fri, 17 Aug 2007 13:32:00 +0800
From:	Herbert Xu <>
To:	Paul Mackerras <>
Cc:	Stefan Richter <>,
	Satyam Sharma <>,
	Christoph Lameter <>,
	"Paul E. McKenney" <>,
	Chris Snook <>,
	Linux Kernel Mailing List <>,,
	Linus Torvalds <>,, Andrew Morton <>,,,,,,,,,,,,
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

On Fri, Aug 17, 2007 at 03:09:57PM +1000, Paul Mackerras wrote:
> Herbert Xu writes:
> > Can you find an actual atomic_read code snippet there that is
> > broken without the volatile modifier?
> There are some in arch-specific code, for example line 1073 of
> arch/mips/kernel/smtc.c.  On mips, cpu_relax() is just barrier(), so
> the empty loop body is ok provided that atomic_read actually does the
> load each time around the loop.

A barrier() is all you need to force the compiler to reread
the value.

The people advocating volatile in this thread are talking
about code that doesn't use barrier()/cpu_relax().

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