On Thu, Aug 16, 2007 at 01:23:06PM +1000, Paul Mackerras wrote:
>
> In particular, atomic_read seems to lend itself to buggy uses. People
> seem to do things like:
>
> atomic_add(&v, something);
> if (atomic_read(&v) > something_else) ...
If you're referring to the code in sk_stream_mem_schedule
then it's working as intended. The atomicity guarantees
that the atomic_add/atomic_sub won't be seen in parts by
other readers.
We certainly do not need to see other atomic_add/atomic_sub
operations immediately.
If you're referring to another code snippet please cite.
> I'd go so far as to say that anywhere where you want a non-"volatile"
> atomic_read, either your code is buggy, or else an int would work just
> as well.
An int won't work here because += and -= do not have the
atomicity guarantees that atomic_add/atomic_sub do. In
particular, this may cause an atomic_read on another CPU
to give a bogus reading.
Cheers,
--
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