linux-kernel - RE: kdump: crash_kexec()-smp_send

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Message-ID: <1319531622.3056.1.camel@br98xy6r>
Date:	Tue, 25 Oct 2011 10:33:42 +0200
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Américo Wang <xiyou.wangcong@...il.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: kdump: crash_kexec()-smp_send_stop() race in panic

Hello Seiji,

On Mon, 2011-10-24 at 18:24 -0400, Seiji Aguchi wrote:
> Hi,
> 
> >> >>> 1st CPU:
> >> >>> panic()->crash_kexec()->mutex_trylock(&kexec_mutex)-> do kdump
> >> >>>
> >> >>> 2nd CPU:
> >> >>> panic()->crash_kexec()->kexec_mutex already held by 1st CPU
> >> >>>        ->smp_send_stop()-> stop CPU 1 (stop kdump)
> >> >>>
> >> >>> How should we fix this problem? One possibility could be to do
> >> >>> smp_send_stop() before we call crash_kexec().
> 
> http://lkml.org/lkml/2010/9/16/353
> 
> I developed a patch solving this issue one year ago.
> (Just adding local_irq_disable in kexec path.)

This won't work (at least on s390) because smp_send_stop() will also
stop CPUs that have interrupts disabled.

Michael

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