linux-kernel - Re: [PATCH] x86_64: remove wrong setting about CONSTANT

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Message-ID: <86802c440802252324u769f087fw83caa26c1960354e@mail.gmail.com>
Date:	Mon, 25 Feb 2008 23:24:56 -0800
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86_64: remove wrong setting about CONSTANT_TSC for intel cpu

On Mon, Feb 25, 2008 at 11:20 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
>  * Yinghai Lu <Yinghai.Lu@....COM> wrote:
>
>
> > also fix error in early_init_intel and reference about x86_capality,
>  > because it is array already.., prevent possible data corruption...
>
>  hm, why should there be data corruption:
>
>
>  > -             set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
>  > +             set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
>
>  cpu_cpu_cap() is currently defined as:
>
>   #define set_cpu_cap(c, bit)     set_bit(bit, (unsigned long *)((c)->x86_capability)
>
>  which is the same. set_cpu_cap() is indeed the cleaner form to do this
>  so your patch is correct as a cleanup.
set_cpu_cap is right
==
set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability); ===> is wrong
should be
set_bit(X86_FEATURE_CONSTANT_TSC, c->x86_capability);

x86_capability is a array ...

so this could prevent some data corruption.

YH
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