linux-kernel - Re: [ANNOUNCE] Merkey's Kernel Debugger

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Message-ID: <48A93CE7.3020301@ah.jp.nec.com>
Date:	Mon, 18 Aug 2008 18:12:07 +0900
From:	Takenori Nagano <t-nagano@...jp.nec.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Andi Kleen <andi@...stfloor.org>, Keith Owens <kaos@....com.au>,
	Jay Lan <jlan@....com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	jmerkey@...fmountaingroup.com,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Josh Boyer <jwboyer@...il.com>, linux-kernel@...r.kernel.org,
	Bernhard Walle <bwalle@...e.de>
Subject: Re: [ANNOUNCE] Merkey's Kernel Debugger

Vivek Goyal wrote:
> On Fri, Aug 08, 2008 at 08:03:03PM +0200, Andi Kleen wrote:
>>> Are you suggesting that kdump should be put onto panic_notifier_list, in
>>> such a way so that it runs last?
>> The point was that kernel debuggers have an at least as legitimate
>> need as kdump to run early on panic as kdump. In particularly they
>> should run before kdump because kdump can be triggered from
>> the debugger.
>>
> 
> Agreed.
> 
>> But for modular kernel debuggers the hook would need to be exported,
>> so in theory everyone could use it. In theory code review should
>> catch that. Another alternative would be to readd the old namespaces
>> patches I posted some time ago, this allowed to export symbols only
>> to specific modules (but that would be also unfortunate for out of tree
>> debuggers) 
>>
> 
> Or an easier way is that debuggers can put a breakpoint on panic().
> 
>> Since we have nearly all other needed hooks for kernel debuggers
>> anyways it doesn't really make sense to stop at panic. So this
>> earlier requirements should be relaxed.
>>
> 
> I think given that so many people want kdump on panic_notifier_list,
> it would be worthwhile to experiment with the different approach.
> 
> - Move kdump to panic_notifier_list.
> - Export panic_notifier_list to user space and provide flexibility
>   so that a user can change the priorities of registered handlers
>   dynamically.
> 
> This will allow an admin to explicitly see who all are goint to run
> in what order in case of panic and also give him capability that he
> can choose to change the order.
> 
> This kind of list should keep all the kind of users happy. Those who
> want to run all the other modules before kdump, they will be able to
> do so and those who don't want, they can boost the priority of kdump
> to put it ahead in the list.
> 
> I think Takenori had some working patches in the past for this. Probably
> time to revisit the patches. (Somebody willing to look into it?).
> 
> Thanks
> Vivek

Hi all,

These are my latest patches. Any comments are welcome.

http://www.gossamer-threads.com/lists/linux/kernel/909582
http://www.gossamer-threads.com/lists/linux/kernel/909581
http://www.gossamer-threads.com/lists/linux/kernel/909584
http://www.gossamer-threads.com/lists/linux/kernel/909583

Thanks,
  Takenori Nagano
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