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

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Date:	Sun, 13 May 2012 15:10:37 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Bojan Smojver <bojan@...ursive.com>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	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 Sunday, May 13, 2012, Bojan Smojver wrote:
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> >On Wednesday, May 09, 2012, Bojan Smojver wrote:
> >> On Wed, 2012-05-09 at 13:40 +0530, Srivatsa S. Bhat wrote:
> >> > > +             error = suspend_devices_and_enter(PM_SUSPEND_MEM);
> >> > 
> >> > 
> >> > I can imagine running into a host of problems here, since the
> >suspend
> >> > sequence is not carried out fully, from the beginning.
> >> > 
> >> > For example, this will skip sending out the PM_SUSPEND_PREPARE and
> >the
> >> > PM_POST_SUSPEND notifiers. Worse, we actually send out the
> >> > PM_HIBERNATION_PREPARE
> >> > and PM_POST_HIBERNATION notifiers and then do a suspend instead,
> >> > underneath!
> >> > 
> >> > (Similar cases for the rest of the notifiers sent during suspend vs
> >> > hibernation).
> >> > 
> >> > Don't we need to handle such things properly, in order to make
> >> > suspend-to-both
> >> > work reliably? 
> >> 
> >> 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.
> >> 
> >> Rafael?
> >
> >Sorry, that has fallen out of my radar somehow.
> >
> >Srivatsa is right, we should generally pay attention to those details.
> >
> >I think we should generally use a different "prepare" notification for
> >the
> >save-image-and-suspend case.
> >
> >Thanks,
> >Rafael
> 
> 
> OK, I will try to rework then, if that is the case.
> 
> What I don't understand is this: should the hibernation fail for some reason,
> we would get the same hibernation code unwind that failure, right?

Yes, if the failure happens before we attempt to suspend.

> So, a suspend after the image write will be just one long "failure", after
> which hibernation code has to unwind again. No?

Hmm.  Good question.  It should be like this I think, although there may be
some corner cases lurking.

Thanks,
Rafael
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