linux-kernel - Re: [PATCH]: In kernel hibernation, suspend to both

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Date:	Mon, 14 May 2012 05:02:54 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Bojan Smojver <bojan@...ursive.com>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux PM list <linux-pm@...r.kernel.org>,
	linux-kernel@...r.kernel.org, bp@...en8.de
Subject: Re: [PATCH]: In kernel hibernation, suspend to both

On 05/09/2012 04:41 PM, Bojan Smojver wrote:

> Bojan Smojver <bojan@...ursive.com> wrote:
> 
>> Honest answer - I have absolutely no idea. I've seen the code of
>> suspend-utils (i.e. user mode stuff) and it seems to me that it does
>> exactly this. Could be wrong of course, just like many times before.
> 
> What makes me think that this may not be that bad is the fact that

> post-resume, it will actually be hibernation code that will be unwinding

> things. So like this: prepare for hibernation, create image, suspend to

> memory 

This is the point where your patch gets scary - Suspend is not carried out
in its fullest sense; instead you jump directly to suspend_devices_and_enter().
Luckily, most of the things that happen before this are common between
suspend and hibernation. However, one thing that really stands out is the
notifications: if you directly call suspend_devices_and_enter(), we end
up missing the PM_SUSPEND_PREPARE notifications.

And there is no guarantee that everybody implements the same thing for
both PM_SUSPEND_PREPARE and PM_HIBERNATION_PREPARE notifications. That is
the reason I don't think it is safe.

> (equivalent to hibernation failure of some kind, really), resume

>from memory, unwind from unsuccessful hibernation.
> 
> No?
> 

Regards,
Srivatsa S. Bhat
IBM Linux Technology Center

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