linux-kernel - Re: kdump hangs up by Sysrq+C trigger in high load.

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Date:	Tue, 16 Dec 2008 12:09:49 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Yoshihiro Takahashi <ytakahashi@...aclelinux.com>
Cc:	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Huang Ying <ying.huang@...el.com>, kexec@...ts.infradead.org,
	Bernhard Walle <bwalle@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: kdump hangs up by Sysrq+C trigger in high load.


* Yoshihiro Takahashi <ytakahashi@...aclelinux.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
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