linux-kernel - Re: [PATCH] "volatile considered harmful", take 3

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Message-ID: <a781481a0705112021u7b6d32fcxb6318d7e2443c970@mail.gmail.com>
Date:	Sat, 12 May 2007 08:51:24 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Jonathan Corbet" <corbet@....net>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	"Johannes Stezenbach" <js@...uxtv.org>,
	"Jesper Juhl" <jesper.juhl@...il.com>,
	"Randy Dunlap" <randy.dunlap@...cle.com>,
	"Heikki Orsila" <shdl@...alwe.fi>,
	"H. Peter Anvin" <hpa@...or.com>,
	"jimmy bahuleyan" <knight.camelot@...il.com>,
	"Stefan Richter" <stefanr@...6.in-berlin.de>
Subject: Re: [PATCH] "volatile considered harmful", take 3

On 5/11/07, Jonathan Corbet <corbet@....net> wrote:
> Here's another version of the volatile document.  Once again, I've tried
> to address all of the comments.  There haven't really been any recent
> comments addressing the correctness of the document; people have been
> more concerned with how it's expressed.  I'm glad to see files in
> Documentation/ held to a high standard of writing, but, unless somebody
> has a factual issue this time around I would like to declare Mission
> Accomplished and move on.

The document looks good, but whether:

> +  - Pointers to data structures in coherent memory which might be modified
> +    by I/O devices can, sometimes, legitimately be volatile.  A ring buffer
> +    used by a network adapter, where that adapter changes pointers to
> +    indicate which descriptors have been processed, is an example of this
> +    type of situation.

is a legitimate use case for volatile is still not clear to me (I
agree with Alan's
comment in a previous thread that this seems to be a case where a memory
barrier would be applicable^Wbetter, actually). I could be wrong here, so
would be nice if Peter explains why volatile is legitimate here.

Otherwise, it's fine with me.

Thanks,
Satyam
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