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

[Herbert Xu <herbert@gondor.apana.org.au>]

On Thu, Aug 16, 2007 at 09:34:41AM -0700, Paul E. McKenney wrote:
>
> The compiler can also reorder non-volatile accesses.  For an example
> patch that cares about this, please see:
> 
> 	http://lkml.org/lkml/2007/8/7/280
> 
> This patch uses an ORDERED_WRT_IRQ() in rcu_read_lock() and
> rcu_read_unlock() to ensure that accesses aren't reordered with respect
> to interrupt handlers and NMIs/SMIs running on that same CPU.

Good, finally we have some code to discuss (even though it's
not actually in the kernel yet).

First of all, I think this illustrates that what you want
here has nothing to do with atomic ops.  The ORDERED_WRT_IRQ
macro occurs a lot more times in your patch than atomic
reads/sets.  So *assuming* that it was necessary at all,
then having an ordered variant of the atomic_read/atomic_set
ops could do just as well.

However, I still don't know which atomic_read/atomic_set in
your patch would be broken if there were no volatile.  Could
you please point them out?

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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