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Date:	Fri, 17 Aug 2007 07:59:02 +0800
From:	Herbert Xu <>
To:	"Paul E. McKenney" <>
Cc:	Stefan Richter <>,
	Paul Mackerras <>,
	Satyam Sharma <>,
	Christoph Lameter <>,
	Chris Snook <>,
	Linux Kernel Mailing List <>,,
	Linus Torvalds <>,, Andrew Morton <>,,,,,,,,,,,,
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

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:
> 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?

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