linux-kernel - Re: [linux-pm] [PATCH] hibernation should work ok with memory hotplug

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Date:	Thu, 06 Nov 2008 13:03:06 +1100
From:	Nigel Cunningham <ncunningham@...a.org.au>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Tolentino <matthew.e.tolentino@...el.com>,
	Hansen <haveblue@...ibm.com>, linux-pm@...ts.osdl.org,
	Matt@...p1.linux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Dave@...p1.linux-foundation.org,
	Mel Gorman <mel@...net.ie>, Andy@...p1.linux-foundation.org,
	Whitcroft <apw@...dowen.org>,
	Yasunori Goto <y-goto@...fujitsu.com>, pavel@...e.cz,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [linux-pm] [PATCH] hibernation should work ok with memory
	hotplug

Hi.

On Thu, 2008-11-06 at 09:53 +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 05 Nov 2008 16:28:01 -0800
> Dave Hansen <dave@...ux.vnet.ibm.com> wrote:
> 
> > On Thu, 2008-11-06 at 09:14 +0900, KAMEZAWA Hiroyuki wrote:
> > > Ok, please consider "when memory hotplug happens." 
> > > 
> > > In general, it happens when
> > >   1. memory is inserted to slot.
> > >   2. the firmware notifes the system to enable already inserted memory.
> > > 
> > > To trigger "1", you have to open cover of server/pc. Do you open pc while the system
> > > starts hibernation ? for usual people, no.
> > 
> > You're right, this won't happen very often.  We're trying to close a
> > theoretical hole that hasn't ever been observed in practice.  But, we
> > don't exactly leave races in code just because we haven't observed them.
> > I think this is a classic race.
> > 
> > If we don't close it now, then someone doing some really weirdo hotplug
> > is going to run into it at some point.  Who knows what tomorrow's
> > hardware/firmware will do?
> > 
> Hmm, people tend to make crazy hardware, oh yes. the pc may fly in the sky with rocket engine.

It doesn't even have to be crazy. Just imagine someone bumping a button
on the case while plugging in the memory and that button being
configured to make the machine hibernate.

Regards,

Nigel

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