linux-kernel - Re: [2.6.25-rc5-mm1] BUG: spinlock bad magic early during boot

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Message-ID: <47EB67AC.4090309@aitel.hist.no>
Date:	Thu, 27 Mar 2008 10:23:56 +0100
From:	Helge Hafting <helge.hafting@...el.hist.no>
To:	Dave Hansen <haveblue@...ibm.com>
CC:	Pavel Machek <pavel@....cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	?ric Piel <Eric.Piel@...mplin-utc.net>,
	Tilman Schmidt <tilman@...p.cc>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Renninger <trenn@...e.de>,
	Len Brown <len.brown@...el.com>,
	Christoph Hellwig <hch@...radead.org>,
	Markus Gaugusch <dsdt@...gusch.at>, linux-acpi@...r.kernel.org,
	Al Viro <viro@...IV.linux.org.uk>,
	Arjan van de Ven <arjanv@...hat.com>,
	Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [2.6.25-rc5-mm1] BUG: spinlock bad magic early during boot

Dave Hansen wrote:
> On Fri, 2008-03-21 at 14:17 +0100, Pavel Machek wrote:
>   
>>> So what's the reason for pushing for this insanely-early workaround in the 
>>> first place, instead of letting user-space do something like
>>>
>>>       cat my-dsdt-image > /proc/sys/acpi/DSDT
>>>
>>> or whatever at runtime?
>>>       
>> You have interpretted code runing (AML), and you want to replace it
>> with different code?
>>
>> Akin to changing from one kernel to different during runtime?
>>     
>
> Heh.  That gave me an idea.
>
> Can we use kexec for this?  Let's say you get as far in boot as the
> initrd and realize that you're running on one of these screwed up
> systems.  Can you stick the new DSDT somewhere known (and safe) in
> memory, and kexec yourself back to the beginning of the kernel boot?
>
> When you boot up the second time, you have the new, shiny DSDT there
> which is, of course, used instead of the bogus BIOS one.
>   
I see a problem here. 
This could work. And if it is successful, the "kexec reboot around 
busted hw"-trick
is used for other stuff as well.

So your broken machine reboots with some fix, then it reboots with the
custom DSDT. Is the previous fix preserved? Then a third problem is hit,
another kexec reboot. Is the first fix _and_ the custom DSDT
preserved on this reboot?  Or do we get an infinite sequence of reboots,
alternating between a couple of completely unrelated fixes for bad 
hw/bios...

Once there is more than one fix utilizing this trick, some "protocol" for
managing a string of  kexec fixes might become necessary.

Helge Hafting

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