linux-kernel - Re: [PATCH v3 2/3] CPU hotplug, Freezer: Synchronize CPU hotplug and freezer

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Date:	Fri, 21 Oct 2011 10:43:39 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
cc:	a.p.zijlstra@...llo.nl, <rjw@...k.pl>, <pavel@....cz>,
	<len.brown@...el.com>, <mingo@...e.hu>,
	<akpm@...ux-foundation.org>, <suresh.b.siddha@...el.com>,
	<lucas.demarchi@...fusion.mobi>, <linux-pm@...r.kernel.org>,
	<rusty@...tcorp.com.au>, <vatsa@...ux.vnet.ibm.com>,
	<ashok.raj@...el.com>, <linux-kernel@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <rdunlap@...otime.net>
Subject: Re: [PATCH v3 2/3] CPU hotplug, Freezer: Synchronize CPU hotplug
 and freezer

On Fri, 21 Oct 2011, Srivatsa S. Bhat wrote:

> Don't allow the freezer subsystem to race with CPU hotplug to ensure that
> during the entire duration for which the CPU hotplug notifications are run,
> the state of the system (with respect to the tasks being frozen or not)
> remains constant.
> 
> This patch introduces four notifications in the freezer subsystem,
> PM_FREEZE_PREPARE, PM_POST_FREEZE, PM_THAW_PREPARE and PM_POST_THAW.
> These help in making other subsystems aware of the freezer's activity.
> The CPU hotplug infrastructure hooks on to these notifications and
> synchronizes with the freezer.

It seems pointless to send out PM_POST_FREEZE and PM_THAW_PREPARE 
notifications.  No task will be running to be affected by them.

Alan Stern

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