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

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Message-ID: <5C4C569E8A4B9B42A84A977CF070A35B2C5756688D@USINDEVS01.corp.hds.com>
Date:	Thu, 20 Oct 2011 11:13:26 -0400
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	Don Zickus <dzickus@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"Chen, Gong" <gong.chen@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	Matthew Garrett <mjg@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"ying.huang@...el.com" <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

Don,

>That is part of the wider problem with kmsg_dump that Vivek talks about
>with me, is that it is just a giant hook in the panic path with limited
>auditing.  So we need to explicit set our expectations with BUG_ONs/WARNs
>otherwise we might get bit later by them.

I found an issue while developing a patch v2.

We can't call BUG_ON(in_nmi() && reason != KMSG_DUMP_PANIC)
because kmsg_dump(KMSG_DUMP_EMERG) is called in NMI context if "panic" kernel parameter is set.

I will keep doing research bust_spinlock() or vprintk() so that lockdep checking works and we can avoid any deadlocks.

Seiji
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