linux-kernel - Re: [RFC PATCH(Experimental) 1/4] freezer-cpu-hotplug core

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Date:	Wed, 14 Feb 2007 23:22:09 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	akpm@...l.org, paulmck@...ibm.com, mingo@...e.hu, vatsa@...ibm.com,
	dipankar@...ibm.com, venkatesh.pallipadi@...el.com,
	linux-kernel@...r.kernel.org, rjw@...k.pl
Subject: Re: [RFC PATCH(Experimental) 1/4] freezer-cpu-hotplug core

On 02/14, Gautham R Shenoy wrote:
>
> o Splits CPU_DEAD into two events namely
>   - CPU_DEAD: which will be handled while the processes are still
>               frozen.
> 
>   - CPU_DEAD_KILL_THREADS: To be handled after we thaw_processes.

Imho, this is not right. This change the meaning of CPU_DEAD, and so
we should fix all users of CPU_DEAD as well.

How about

	CPU_DEAD_WHATEVER
		the processes are still frozen

	CPU_DEAD
		after we thaw_processes

This way we can add processing of the new CPU_DEAD_WHATEVER event where
it may help. We don't need to change (for example) workqueue.c with this
patch, we can do it in a separate patch.

CPU_UP_PREPARE is called after freeze_processes()... Probably this works,
but imho this is no good. Suppose for a moment that khelper will be frozen
(yes, yes it can't be), then we can't do kthread_create().

Oleg.

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