linux-kernel - Re: atomics: document that linux expects certain atomic behaviour from unsigned long

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Message-ID: <20090103202740.GC1666@elf.ucw.cz>
Date:	Sat, 3 Jan 2009 21:27:40 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, mtk.manpages@...il.com,
	rdunlap@...otime.net, linux-doc@...r.kernel.org
Subject: Re: atomics: document that linux expects certain atomic behaviour
	from unsigned long

On Sat 2009-01-03 20:19:55, Alan Cox wrote:
> On Sat, 3 Jan 2009 13:44:00 +0100
> Pavel Machek <pavel@...e.cz> wrote:
> 
> > Linux relies on unsigned long to behave like atomic for read/write.
> 
> Actually it isn't that simple and this advice shouldn't be given IMHO.
> 
> unsigned long is not the same as atomic in several respects including
> ordering and caching of the result.

Ok... I keep seeing patches using int/long instead of atomic and
claiming that it is okay.

If it is okay and linux relies on it, it should be documented.

If it is not okay, I guess we should document it, too -- it seems to
be common mistake. 

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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