Re: [PATCH] stop on cpu lost

[Andrew Morton]

On Tue, 20 Jun 2006 12:51:59 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:

> When the application is mis-configurated at cpu hot removal, a task's 
> cpus_allowd can be empty. this patch adds sysctl to stop tasks whose 
> cpus_allowed is empty.
> 
> I think there isn't one good answer to handle this problem and this is
> depend on system management policy. In a system, forced migration is better 
> than stop. In another, stopping tasks (and killing) will meet requirement.
> 
> How about this ?
> 
> -Kame
> 
> Now, when a task loses all of its allowed cpus because of cpu hot removal,
> it will be foreced to migrate to not-allowed cpus.
> 
> In this case, the task is not properly reconfigurated by a user before
> cpu-hot-removal. Here, the task (and system) is in a unexpeced wrong state.
> This migration is maybe one of realistic workarounds. But sometimes it will be
> harmfull.
> (stealing other cpu time, making bugs in thread controllers, do some unexpected
>  execution...)
> 
> This patch adds sysctl "sigstop_on_cpu_lost". When sigstop_on_cpu_lost==1,
> a task which losts is cpu will be stopped by SIGSTOP.
> Depends on system management policy, mis-configurated applications are stopped.
> 

Well that's a pretty unpleasant patch, isn't it?

But I guess it's policy, and if we cannot think of anything better then we'll
have to do it this way :(

> 
> 
>  include/linux/sysctl.h |    1 +
>  kernel/sched.c         |   14 ++++++++++++++
>  kernel/sysctl.c        |   14 ++++++++++++++

An update to Documentation/cpu-hotplug.txt would seem appropriate, please, and a
line in Documentation/sysctl/kernel.txt which refers to it.
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