linux-kernel - RE: SMP share data declaration

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Message-ID: <D269C7CBDF116A48982D4DC51F111BE30213AF1C@nsezhpmail01.india.ipolicynet.com>
Date:	Fri, 14 Jul 2006 17:01:59 +0530
From:	"Hannibal B" <bhannibal@...licynetworks.com>
To:	"Jesper Juhl" <jesper.juhl@...il.com>, <wyb@...sec.com.cn>
Cc:	<linux-kernel@...r.kernel.org>
Subject: RE: SMP share data declaration

Spinlocks would be the one to protect the variable and synchronies
between CPU, But it's a busy waiting mechanism(just a word of caution).
Regards,
Hannibal

-----Original Message-----
From: Jesper Juhl [mailto:jesper.juhl@...il.com] 
Sent: Friday, July 14, 2006 2:18 PM
To: wyb@...sec.com.cn
Cc: linux-kernel@...r.kernel.org
Subject: Re: SMP share data declaration

On 14/07/06, wyb@...sec.com.cn <wyb@...sec.com.cn> wrote:
> I know that an integer variable should be declared volatile to share
between
> CPUs.

NO. volatile won't protect you sufficiently.

Use spinlocks, mutexes, semaphores, barriers and the like to protect
variables from concurrent access. Using volatile for this is a BUG and
it won't work correctly.


-- 
Jesper Juhl <jesper.juhl@...il.com>
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