linux-kernel - Re: Regression: BUG when battery is removed before resuming from hibernation

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Date:	Wed, 09 Jun 2010 10:07:20 +0100
From:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Kernel Testers List <kernel-testers@...r.kernel.org>,
	linux acpi <linux-acpi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Regression: BUG when battery is removed before resuming from
 hibernation

Rafael J. Wysocki wrote:
> On Tuesday 08 June 2010, Alan Jenkins wrote:
>   
>> I found this bug 2.6.34 on my Asus EeePC 701 (x86_32 arch).  It didn't 
>> happen to me before, when I was running nearly-2.6.33 or 2.6.32-release.
>>
>> I used git-bisect, but unfortunately the result isn't very helpful.  My 
>> next step will be to try to narrowing down the culprits by disabling 
>> individual CONFIG options.  Here are my results so far, in case anyone 
>> is interested.
>>
>>
>> == Steps to reproduce ==
>>
>> I) Boot off mains power, with battery removed.  Login to KDE4 session, 
>> with Konsole as the only running application.
>> II) Run "sudo pm-hibernate"
>>
>> 1. When the system switches to text mode (a.k.a the console), 
>> immediately insert the battery.
>> 2. Once the system has fully hibernated, remove the battery.
>> 3. Press the power button to resume.  The backtrace below is generated 
>> during resume.
>>     
>
> You're not supposed to be doing that.
>
> Rafael
>   

I take it you mean "don't plug devices in during hibernation; you'll run 
out of memory, Bad Things will happen, and you can expect resume to 
fail".  Pity.  It wasn't an artificial test case, just an unusual usage 
pattern of mine[1].

I guess it wouldn't be guaranteed safe even if I was plugging the device 
in first.  The battery connection could take a few seconds to stabilize, 
and there's software equivalents in things like the usb-storage delay.

I can't complain about safety margins; other people might want to do 
similar things with an entire docking station...

Any chance of a big screaming warning?  IIRC there's one global flag to 
fail userspace call-outs while userspace is frozen.  Would it be 
acceptable to document this in code & behaviour by aborting the 
hibernation on hot-plug?  (hot-*un*plug would presumably be allowed).

Alan

[1] I do this for conservation.  I'm told batteries last longer if I 
don't use them & let them get warm.  I put the battery in for 
hibernation so I can remove mains power without waiting.  I start 
hibernation first, because in practice you have to have the screen 
closed in order to plug or unplug the battery.
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