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

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().

Cheers,
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