linux-kernel - Re: [Patch V1 1/3] x86, mce: MCE log size not enough for high core parts

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Message-ID: <20150924210732.GM3774@pd.tnic>
Date:	Thu, 24 Sep 2015 23:07:33 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"Raj, Ashok" <ashok.raj@...el.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: Re: [Patch V1 1/3] x86, mce: MCE log size not enough for high core
 parts

On Thu, Sep 24, 2015 at 01:22:12PM -0700, Raj, Ashok wrote:
> Another reason i had a separate buffer in my earlier patch was to avoid 
> calling rcu() functions from the offline CPU. I had an offline discussion 
> with Paul McKenney  he said don't do that... 
> 
> mce_gen_pool_add()->gen_pool_alloc() which calls rcu_read_lock() and such. 
> So it didn't seem approprite.

How are you ever going to call into those from an offlined CPU?!

And that's easy:

	if (!cpu_online(cpu))
		return;

> Also the function doesn't seem safe to be called in NMI context. Although

That's why it is a lockless buffer - we added it *exactly* because we didn't
want to call printk in an NMI context. So please expand...

> MCE is different, for all intentional purposes we should treat both as same
> priority. The old style log is simple and tested in those cases.
> 
> I like everything you say below... something we could do as our next phase
> of improving logging and might need more careful work to build it right.
> 
> just like how MC banks have overwrite rules, we can possibly do something
> like that if the buffer fills up.

Right.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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