linux-kernel - Re: [PATCH v2 1/2] Replace if statement with WARN_ON_ONCE() in cmci

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Date:	Fri, 19 Oct 2012 18:40:45 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	stable@...r.kernel.org, tony.luck@...el.com, bp@...64.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	miaox@...fujitsu.com, laijs@...fujitsu.com, wency@...fujitsu.com,
	x86@...nel.org, linux-edac@...r.kernel.org,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v2 1/2] Replace if statement with WARN_ON_ONCE() in
 cmci_rediscover().

On Fri, Oct 19, 2012 at 01:45:27PM +0800, Tang Chen wrote:
> cmci_rediscover() is only called by the CPU_POST_DEAD event handler,
> which means the corresponding cpu has already dead. As a result, it
> won't be accessed in the for_each_online_cpu loop.
> So, we could change the if(cpu == dying) statement into a WARN_ON_ONCE().
> 
> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
> ---
>  arch/x86/kernel/cpu/mcheck/mce_intel.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mcheck/mce_intel.c b/arch/x86/kernel/cpu/mcheck/mce_intel.c
> index 38e49bc..481d152 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce_intel.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce_intel.c
> @@ -180,8 +180,8 @@ void cmci_rediscover(int dying)
>  	cpumask_copy(old, &current->cpus_allowed);
>  
>  	for_each_online_cpu(cpu) {
> -		if (cpu == dying)
> -			continue;
> +		WARN_ON_ONCE(cpu == dying);

Ok, I don't understand that:

we want to warn that the rediscovering is happening on a dying cpu?? And
before that, we simply jumped over it and didn't do the rediscovering
there? Why should we warn at all?

Huh?

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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