Re: [PATCH 6/24] make atomic_read() behave consistently on frv

Herbert Xu
2007-08-13T05:17:23Z

Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> On Sat, Aug 11, 2007 at 08:54:46AM +0800, Herbert Xu wrote:
>> Chris Snook <csnook@redhat.com> wrote:
>> >
>> > cpu_relax() contains a barrier, so it should do the right thing. For
>> > non-smp architectures, I'm concerned about interacting with interrupt
>> > handlers. Some drivers do use atomic_* operations.
>>
>> What problems with interrupt handlers? Access to int/long must
>> be atomic or we're in big trouble anyway.
>
> Reordering due to compiler optimizations. CPU reordering does not
> affect interactions with interrupt handlers on a given CPU, but
> reordering due to compiler code-movement optimization does. Since
> volatile can in some cases suppress code-movement optimizations,
> it can affect interactions with interrupt handlers.

If such reordering matters, then you should use one of the
*mb macros or barrier() rather than relying on possibly
hidden volatile cast.

Cheers,
--
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