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

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Date:	Fri, 30 Jan 2015 12:47:39 +0000 (GMT)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	James Hogan <james.hogan@...tec.com>
cc:	Aaro Koskinen <aaro.koskinen@....fi>,
	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

On Fri, 30 Jan 2015, James Hogan wrote:

> >  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.

 Ah, I see, thanks for enlightening me.  But in that case wouldn't it be 
possible to postpone console output from `printk' until it is safe to 
access the device?  In a manner similar to how for example we handle calls 
to `printk' made from the hardirq context.  That would make things less 
fragile.

  Maciej
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