linux-kernel - Re: [-mm patch] enforce noreplace-smp in alternative

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Message-Id: <20070823145038.9895784f.akpm@linux-foundation.org>
Date:	Thu, 23 Aug 2007 14:50:38 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Frederik Deweerdt <deweerdt@...e.fr>
Cc:	linux-kernel@...r.kernel.org, jeremy@...p.org
Subject: Re: [-mm patch] enforce noreplace-smp in alternative_instructions()

On Wed, 22 Aug 2007 22:25:51 +0200
Frederik Deweerdt <deweerdt@...e.fr> wrote:

> On Wed, Aug 22, 2007 at 02:06:48AM -0700, Andrew Morton wrote:
> > 
> > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc3/2.6.23-rc3-mm1/
> > 
> Hi Jeremy,
> 
> arch/i386/kernel/alternative.c:alternative_instructions() doesn't
> check for noreplace-smp before setting capability bits and freeing the
> __smp_locks section.

umm, so?  What happens then?  What bug is being fixed here, and what are
its consequences?

> Every call to alternatives_smp_unlock() checks for noreplace-smp
> beforehand, so remove the check from there.
> 
> Boot tested on i386 with UP+noreplace-smp (lguest) and SMP (real hardware)
> 
> Regards,
> Frederik
> 
> Signed-off-by: Frederik Deweerdt <frederik.deweerdt@...il.com>
> 
> diff --git a/arch/i386/kernel/alternative.c b/arch/i386/kernel/alternative.c
> index 9f4ac8b..7c5af80 100644
> --- a/arch/i386/kernel/alternative.c
> +++ b/arch/i386/kernel/alternative.c
> @@ -221,9 +221,6 @@ static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end
>  	u8 **ptr;
>  	char insn[1];
>  
> -	if (noreplace_smp)
> -		return;
> -
>  	add_nops(insn, 1);
>  	for (ptr = start; ptr < end; ptr++) {
>  		if (*ptr < text)
> @@ -406,7 +403,7 @@ void __init alternative_instructions(void)
>  #endif
>  
>  #ifdef CONFIG_SMP
> -	if (smp_alt_once) {
> +	if (smp_alt_once && !noreplace_smp) {
>  		if (1 == num_possible_cpus()) {
>  			printk(KERN_INFO "SMP alternatives: switching to UP code\n");
>  			set_bit(X86_FEATURE_UP, boot_cpu_data.x86_capability);

You refer to rc3-mm1 and this is described as a "-mm patch" but it seems to
also be applicable to mainline?
-
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