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

[Herbert Xu]

On Thu, Aug 16, 2007 at 02:11:43PM +1000, Paul Mackerras wrote:
>
> The uses of atomic_read where one might want it to allow caching of
> the result seem to me to fall into 3 categories:
> 
> 1. Places that are buggy because of a race arising from the way it's
>    used.
> 
> 2. Places where there is a race but it doesn't matter because we're
>    doing some clever trick.
> 
> 3. Places where there is some locking in place that eliminates any
>    potential race.

Agreed.

> In case 1, adding volatile won't solve the race, of course, but it's
> hard to argue that we shouldn't do something because it will slow down
> buggy code.  Case 2 is hopefully pretty rare and accompanied by large
> comment blocks, and in those cases caching the result of atomic_read
> explicitly in a local variable would probably make the code clearer.
> And in case 3 there is no reason to use atomic_t at all; we might as
> well just use an int.

Since adding volatile doesn't help any of the 3 cases, and
takes away optimisations from both 2 and 3, I wonder what
is the point of the addition after all?

Cheers,
-- 
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