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Date: Wed, 17 Dec 2008 16:42:43 +0900
From: Yoshihiro Takahashi <ytakahashi@miraclelinux.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Eduardo Habkost <ehabkost@redhat.com>,
        Huang Ying <ying.huang@intel.com>, kexec@lists.infradead.org,
        Bernhard Walle <bwalle@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: kdump hangs up by Sysrq+C trigger in high load.
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Ingo. Thank you, your reply.

I will serch it again.

On Tue, 16 Dec 2008 12:09:49 +0100
Ingo Molnar <mingo@elte.hu> wrote:

> 
> * Yoshihiro Takahashi <ytakahashi@miraclelinux.com> wrote:
> 
> > Hi.
> > 
> > kdump hangs up by Sysrq+C trigger once in about 10 times in high load. 
> > After the above occurs, kdump cannot collect vmcores with NMI button. 
> > When waiting_for_crash_ipi does case more than 0, mdelay seem to make a 
> > stall.
> > 
> > While nmi_shootdown_cpus(), mdelay may not work since interruption is 
> > disable.  (ex. when crashing kernel by NMI interruption, all 
> > interruption may be disabled.).
> > 
> > So I think that it should use other way (TSC) instead of mdelay() in 
> > nmi_shootdown_cpus().
> 
> mdelay uses either the tsc or CPU loops - neither stop while IRQs are 
> disabled.
> 
> Could you figure out exactly why it hangs in your case?
> 
> 	Ingo