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Message-ID: <1319531622.3056.1.camel@br98xy6r>
Subject: RE: kdump: crash_kexec()-smp_send_stop() race in panic
From: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Reply-To: holzheu@linux.vnet.ibm.com
To: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Vivek Goyal <vgoyal@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        =?ISO-8859-1?Q?Am=E9rico?= Wang <xiyou.wangcong@gmail.com>,
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Date: Tue, 25 Oct 2011 10:33:42 +0200
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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