linux-kernel - Re: [PATCH] hardlockup: detect hard lockups without NMIs using secondary cpus

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Date:	Thu, 10 Jan 2013 14:22:45 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Colin Cross <ccross@...roid.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	liu chuansheng <chuansheng.liu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] hardlockup: detect hard lockups without NMIs using
	secondary cpus

On Thu, Jan 10, 2013 at 09:02:15AM -0500, Don Zickus wrote:
> On Wed, Jan 09, 2013 at 05:57:39PM -0800, Colin Cross wrote:
> > Emulate NMIs on systems where they are not available by using timer
> > interrupts on other cpus.  Each cpu will use its softlockup hrtimer
> > to check that the next cpu is processing hrtimer interrupts by
> > verifying that a counter is increasing.
> > 
> > This patch is useful on systems where the hardlockup detector is not
> > available due to a lack of NMIs, for example most ARM SoCs.
> 
> I have seen other cpus, like Sparc I think, create a 'virtual NMI' by
> reserving an IRQ line as 'special' (can not be masked).  Not sure if that
> is something worth looking at here (or even possible).

No it isn't, because that assumes that things like spin_lock_irqsave()
won't mask that interrupt.  We don't have the facility to do that.
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