linux-kernel - RE: [RFC][PATCH -next] make pstore/kmsg_dump run after stopping other cpus in panic path

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Message-ID: <5C4C569E8A4B9B42A84A977CF070A35B2C5747E25E@USINDEVS01.corp.hds.com>
Date:	Mon, 17 Oct 2011 13:34:20 -0400
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	Don Zickus <dzickus@...hat.com>, "Luck, Tony" <tony.luck@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Chen, Gong" <gong.chen@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Brown, Len" <len.brown@...el.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"hughd@...omium.org" <hughd@...omium.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"namhyung@...il.com" <namhyung@...il.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: [RFC][PATCH -next] make pstore/kmsg_dump run after stopping
 other cpus in panic path

Hi,

I agree with Tony's concern.
But as Don told,  the best way to go proceed is fixing backend drivers step by step.

Seiji


>-----Original Message-----
>From: Don Zickus [mailto:dzickus@...hat.com]
>Sent: Monday, October 17, 2011 1:22 PM
>To: Luck, Tony
>Cc: Seiji Aguchi; linux-kernel@...r.kernel.org; Matthew Garrett; Vivek Goyal; Chen, Gong; Andrew Morton; Brown, Len; Huang,
>Ying; ak@...ux.intel.com; hughd@...omium.org; mingo@...e.hu; jmorris@...ei.org; a.p.zijlstra@...llo.nl;
>namhyung@...il.com; dle-develop@...ts.sourceforge.net; Satoru Moriya
>Subject: Re: [RFC][PATCH -next] make pstore/kmsg_dump run after stopping other cpus in panic path
>
>On Mon, Oct 17, 2011 at 09:56:50AM -0700, Luck, Tony wrote:
>> > All this lock busting probably isn't pretty and causes one to reflect what
>> > is going on here.  But as long as we are going to keep the kmsg_dump
>> > design, changes like this seem necessary to make sure the locking stays
>> > sane(r) for now.
>>
>> So should we let the back-end know that locks have been busted?  I worry
>> that we'll get through the pstore layer by blasting away at any locks that
>> get in our way - but then the backend (which may well have been written on
>> the assumption that pstore serialized calls to it) will not do anything
>> useful (and may cause its own hang).
>
>I was kinda alluding to something like that, when I said we probably need
>follow on patches to clean up the backend.  But maybe it would be smarter
>to set a flag in pstore to let the backend know we busted the locks
>instead of letting them do panic checks themselves.  I agree with your
>concerns.
>
>I really can't think of a good overall solution other than slowly
>step-by-step untangle things by making subtle changes, this round being
>the serialization of kmsg_dump().
>
>My brain is to small to figure this out.  I keep thinking about making an
>ascii art diagram to see all the various paths and their contexts, but
>then I keep finding more interesting things to do. :-)
>
>Perhaps we should do that and make some rules about what the back-end can
>and can not do when plugging into kmsg_dump.
>
>Cheers,
>Don

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