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

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Message-ID: <508744ED.2040002@cn.fujitsu.com>
Date:	Wed, 24 Oct 2012 09:31:25 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	"Luck, Tony" <tony.luck@...el.com>
CC:	Borislav Petkov <bp@...en8.de>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"miaox@...fujitsu.com" <miaox@...fujitsu.com>,
	"laijs@...fujitsu.com" <laijs@...fujitsu.com>,
	"wency@...fujitsu.com" <wency@...fujitsu.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] Replace if statement with WARN_ON_ONCE() in cmci_rediscover().

Hi Luck, Borislav,

OK, since you all think it is not necessary, I think I will drop patch1.
And thanks for your comments. :)

So, how about patch2 ?
If you need more detail, please tell me. Thanks. :)

On 10/24/2012 12:16 AM, Luck, Tony wrote:
>> First of all, I do think I was answering your question. As I said
>> before, if an online cpu == dying here, there must be something wrong.
>> Am I right here ?
>
> Yes - but there is a fuzzy line over where it is good to check for "something wrong"
> or whether to trust that the caller of the function knew what they were doing.
>
> For example we trust that "dying" is a valid cpu number.  If we were
> super-paranoid that someone might change the code and call us with a
> bad argument, we might add:
>
> 	BUG_ON(dying<  0 || dying>= MAX_NR_CPUS);
>
> This would certainly help debug the case if someone did make a bogus
> change ... but I think it is clear that this test is way past the fuzzy line and
> into pointless.
>
> Back to the case in question: do we think there is a credible case where
> the "dying" cpu can show up in our "for_each_cpu_online()" loop? The
> original author of the code was worried enough to make a test, but thought
> that the appropriate action was to silently skip it. You want to add a WARN_ON,
> which will cause users who read the console logs to worry, but that most users
> will never see.
>
> -Tony


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