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

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Message-ID: <alpine.DEB.1.10.0901031459010.23262@asgard.lang.hm>
Date:	Sat, 3 Jan 2009 15:01:48 -0800 (PST)
From:	david@...g.hm
To:	Pavel Machek <pavel@...e.cz>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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, 3 Jan 2009, Pavel Machek wrote:

> On Sat 2009-01-03 20:30:44, Alan Cox wrote:
>>> 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.
>>
>> A lot of old code did it knowing it was under the BKL, outside of the BKL
>> its a very bad idea. There were lots of them in the tty layer and I don't
>> doubt there are some left I missed too 8(
>
> I have seen this in new code (some LED driver last time), definitely
> no BKL.
>
> Is there concrete architecture where it breaks? I'd expect i386/x86-64
> to be safe, and pretty much everyone to be safe as long as that long
> is aligned.... or that was the result of arch-maintainers
> discussion...
>
> I'd really like to document if it is right or not, so that I can point
> people to documentation...

you may want to take a look at the new C/C++/POSIX standards (some just 
standardized, some still in development), they explicitly address this 
area.

David Lang
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