linux-kernel - Re: Fw: Re: [mm PATCH 4/6] RCU: (now) CPU hotplug

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Date:	Tue, 30 Jan 2007 10:27:18 -0800
From:	Andrew Morton <akpm@...l.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	paulmck@...ux.vnet.ibm.com, Ingo Molnar <mingo@...e.hu>,
	dipankar@...ibm.com, Gautham Shenoy <ego@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Fw: Re: [mm PATCH 4/6] RCU: (now) CPU hotplug

On Tue, 30 Jan 2007 17:44:47 +0100
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> > I need to look at all uses of PF_NOFREEZE -- as I understand the
> > code, processes marked PF_NOFREEZE will continue running, potentially
> > interfering with the hotplug operation.  :-(
> > 
> > I will pass my findings on to this list.
> 
> Well, I did it some time ago, although not very thoroughly.
> 
> AFAICS there are not so many, but one that stands out is the worker threads.
> We needed two of them to actually go to sleep, so now it's possible to create
> a "freezeable workqueue" the worker thread of which will not set PF_NOFREEZE,
> but currently this is only used by XFS.

Or we can create a variant of freeze_processes which ignores PF_NOFREEZE.

As I said eariler, we might need to change the freezer code for this
application.  In fact we should do so: that sys_sync() call in there is
quite inappropriate, as is, I suppose, the two-pass freeze attempt.  As are
the nice printks, come to that.


Pretty simple stuff though.

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