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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Oleg Nesterov <oleg@tv-sign.ru>
Subject: Re: [PATCH] kthread: Don't depend on work queues
Date: Wed, 11 Apr 2007 21:37:21 +0200
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Cc: Gautham R Shenoy <ego@in.ibm.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Davide Libenzi <davidel@xmailserver.org>,
       Jan Engelhardt <jengelh@linux01.gwdg.de>, Ingo Molnar <mingo@elte.hu>,
       Linus Torvalds <torvalds@linux-foundation.org>,
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       "Serge E. Hallyn" <serge@hallyn.com>, linux-kernel@vger.kernel.org,
       vatsa@in.ibm.com
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On Wednesday, 11 April 2007 16:36, Oleg Nesterov wrote:
> On 04/11, Gautham R Shenoy wrote:
> > On Wed, Apr 11, 2007 at 03:48:05PM +0400, Oleg Nesterov wrote:
> > > On 04/11, Gautham R Shenoy wrote:
> > > >
> > > > On Wed, Apr 11, 2007 at 12:13:34PM +0200, Rafael J. Wysocki wrote:
> > > > > 
> > > > > It should be calling try_to_freeze() somewhere anyway.  We may need to freeze
> > > > > all tasks in some cases.
> > > > 
> > > > How about
> > > > for (;;) {
> > > > 	try_to_freeze();
> > > > 
> > > > ?
> > > 
> > > Why?
> > 
> > If some event (defintely NOT cpu hotplug) needs this thread frozen.
> > 
> > > 
> > > > This change allows us to make all the worker threads freezeable by default.
> > > > >From cpu-hotplug perspective, helper_wq was the only singlethreaded
> > > > non-freezeable workqueue.
> > > 
> > > I think Eric's patch is what you need. We should _not_ freeze kthreadd(), we
> > > need kthread_create() after freezing. Now it doesn't depend on workqueues, we
> > > can freeze them all, single-thread or not.
> > > 
> > 
> > These were my exact thoughts. 
> 
> Sorry, I misunderstood your message.
> 
> Yes, we can freeze it with FE_HOTPLUG_CPU. In that case wait_event()
> should also check !freezing(), and try_to_freeze() should be called
> after case wait_event().
> 
> On the other hand, if "kthreadd" does not sleep on kthread_create_work,
> we have another unfrozen process waiting for kthread_create_info.done.
> So, is there any practical reason why kthreadd() should explicitely go
> to refrigerator?

Good question.  Right now, there probably is not any.

Greetings,
Rafael