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

Herbert Xu writes:

On Fri, Aug 17, 2007 at 03:09:57PM +1000, Paul Mackerras wrote:

quoted

Herbert Xu writes:

quoted

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().

Did you look at it?  Here it is:

	/* Someone else is initializing in parallel - let 'em finish */
	while (atomic_read(&idle_hook_initialized) < 1000)
		;

Paul.