linux-kernel - Re: [PATCH v2 2/2] MIPS: fix kernel lockup or crash after CPU offline/online

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Message-ID: <54CB5B59.5050203@imgtec.com>
Date:	Fri, 30 Jan 2015 10:22:17 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Aaro Koskinen <aaro.koskinen@....fi>
CC:	Ralf Baechle <ralf@...ux-mips.org>,
	David Daney <david.daney@...ium.com>,
	<linux-mips@...ux-mips.org>, <linux-kernel@...r.kernel.org>,
	Hemmo Nieminen <hemmo.nieminen@....fi>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] MIPS: fix kernel lockup or crash after CPU offline/online

Hi Maciej,

On 30/01/15 09:25, Maciej W. Rozycki wrote:
> On Thu, 15 Jan 2015, Aaro Koskinen wrote:
> 
>> As printk() invocation can cause e.g. a TLB miss, printk() cannot be
>> called before the exception handlers have been properly initialized.
>> This can happen e.g. when netconsole has been loaded as a kernel module
>> and the TLB table has been cleared when a CPU was offline.
> 
>  Hmm, why can a call to `printk' cause a TLB miss, what's so special about 
> this function?  Does it use kernel mapped addresses for any purpose such 
> as `vmalloc'?

It would be the fact netconsole (or whatever other console is in use) is
built as a kernel module, memory for which is allocated from the vmalloc
area.

Cheers
James


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