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Re: hard lockup problem

To: Lin Ming <>
Subject: Re: hard lockup problem
From: Ralf Baechle <>
Date: Thu, 18 Apr 2013 14:44:55 +0200
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On Thu, Apr 18, 2013 at 03:13:55PM +0800, Lin Ming wrote:

> I encounter a problem that cpu stuck with irq disabled, which is known
> as hard lockup.
> I know there is NMI hard lockup detector for x86, which can dump the
> back trace of the hard lockup.
> Is there any similar feature for MIPS?

No, there isn't, unfortunately.

This is because on MIPS an NMI is very different from for example x86.
An NMI goes straight to a firmware address and most firmware implementations
don't provided a suitable hook for an OS to gain control back from an NMI.

Generally on MIPS NMIs are used to signal catastrophic problems, things
like a machine check exception but external to the CPU.

One of the notable exceptions is Octeon where (see the Octeon watchdog
driver) an OS can regain control after an NMI.  Malta and SGI IP27 also
have somewhat useful NMIs.


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