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Message-ID: <1319772566.6759.27.camel@deadeye>
Subject: Re: [RFC] should VM_BUG_ON(cond) really evaluate cond
From: Ben Hutchings <bhutchings@solarflare.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
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Date: Fri, 28 Oct 2011 04:29:26 +0100
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On Fri, 2011-10-28 at 04:52 +0200, Eric Dumazet wrote:
> Le vendredi 28 octobre 2011 à 02:44 +0100, Ben Hutchings a écrit :
> 
> > Whether or not it needs to provide any ordering guarantee, atomic_read()
> > must never read more than once, and I think that requires the volatile
> > qualification.  It might be clearer to use the ACCESS_ONCE macro,
> > however.
> > 
> 
> Where this requirement comes from ?

That is the conventional behaviour of 'atomic' operations, and callers
may depend on it.

> Maybe then introduce atomic_read_once() for users really needing it :)
>
> ACCESS_ONCE will force the read/move instruction I try to avoid :(
[...]

I'm sure you can find some other way to avoid it.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.