linux-kernel - Re: [linux-pm] Fundamental flaw in system suspend, exposed by freezer removal

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Message-ID: <47C415F2.2060905@davidnewall.com>
Date:	Wed, 27 Feb 2008 00:06:50 +1030
From:	David Newall <davidn@...idnewall.com>
To:	David Brownell <david-b@...bell.net>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-pm@...ts.linux-foundation.org,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [linux-pm] Fundamental flaw in system suspend, exposed by freezer
 removal

David Brownell wrote:
> On Tuesday 26 February 2008, David Newall wrote:
>   
>> Hardware can be inserted and removed while we're in a suspend state; and
>> there's nothing that we can do about it until we resume.  Is it fair to
>> say, then, that having started suspend, we could reasonably ignore any
>> device insertion and removal, and handle it on resume?
>>     
>
> "Ignore" seems a bit strong; those events may be wakeup triggers,
> which would cause the hardware to make it a very short suspend state.
>
> "Defer handling" is more to the point, be it by hardware or software.
>
>   

Of course, "defer".  The insertion has to be handled eventually.  What
I'm wondering is if we can ignore it, and catch it on the resume.


>> Presumably we need to scan for hardware changes on resume.
>>     
>
> Not on most busses I work with; the hardware issues notifications
> whenever the devices are removable.
>   

There's no notification while we're suspended.  Isn't it necessary to
scan all busses on resume, just to know what's on them?
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