linux-kernel - Re: [PATCH] Softlockup (out of cpu) killer

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Date:	Mon, 12 Dec 2011 01:28:29 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Vincent Li <vincent.mc.li@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Don Zickus <dzickus@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mandeep Singh Baines <msb@...omium.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Softlockup (out of cpu) killer

On Sun, Dec 11, 2011 at 02:48:55PM -0800, Vincent Li wrote:
> In kernel, there is out of memory (OOM) killer, why not make an out of cpu (OOC) killer?
> I tested following patch by running an user-space cpu hogging process and the softlockukp
> detector killed the process successfully.
> 
>  Softlockup could be caused by user-space process hogging cpu, add softlockup_kill kernel
>  config to allow kernel to kill the user space cpu hogging process. this feature is
>  useful for high availability systems that have uptime gurantees and where a softlockup
>  must be resolved ASAP
> 
> echo 1 > /proc/sys/kernel/softlockukp_kill to enable cpu hog process killer
> echo 0 > /proc/sys/kernel/softlockup_kill to disable cpu hog process killer

That assumes a signal would be enough to pull a process out of its softlockup.
I believe this is seldom the case. A process in a softlockup is stuck in some
place that has preemption disabled. Unless it luckily polls there for pending
signals, that won't work.

But may be that happens more often than I think. May be other people have
more insight.
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