linux-kernel - Re: [PATCH v2 1/3] PM suspend/hibernate: Call notifier after freezing processes

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Message-Id: <201612271529.59652@pali>
Date:   Tue, 27 Dec 2016 15:29:59 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     NeilBrown <neilb@...e.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, Neil Brown <neilb@...e.de>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        dm-devel@...hat.com, linux-raid@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] PM suspend/hibernate: Call notifier after freezing processes

On Wednesday 22 July 2015 01:03:23 Rafael J. Wysocki wrote:
> On Wed, Jul 22, 2015 at 1:00 AM, Rafael J. Wysocki <rafael@...nel.org>
> wrote:
> > Hi Neil,
> > 
> > On Wed, Jul 22, 2015 at 12:08 AM, NeilBrown <neilb@...e.com> wrote:
> >> On Mon, 20 Jul 2015 23:46:32 +0200 "Rafael J. Wysocki"
> >> 
> >> <rjw@...ysocki.net> wrote:
> >>> On Monday, July 20, 2015 09:32:26 AM Pali Rohár wrote:
> >>> > On Saturday 18 July 2015 01:27:15 Rafael J. Wysocki wrote:
> >>> > > On Thursday, July 16, 2015 09:33:02 AM Pali Rohár wrote:
> >>> > > > On Thursday 16 July 2015 03:02:03 Rafael J. Wysocki wrote:
> >>> > > > > Also, if you're adding AFTER_FREEZE, it would be good to
> >>> > > > > add BEFORE_THAW too for symmetry.
> >>> > > > 
> >>> > > > But there is no use case for BEFORE_THAW. At least it is
> >>> > > > not needed for now.
> >>> > > 
> >>> > > For your use case, a single function pointer would be
> >>> > > sufficient too.
> >>> > 
> >>> > What do you mean by single function pointer? kernel/power is
> >>> > part of kernel image and dm-crypt is external kernel module.
> >>> 
> >>> Well, if there is a function pointer in the core suspend code
> >>> initially set to NULL and exported to modules such that the
> >>> dm-crypt code can set it to something else, that should be
> >>> sufficient, shouldn't it?
> >> 
> >> As long as the dm-crypt module is never unloaded.
> > 
> > OK, there is a race related to that.
> > 
> >> And as long as no other module could very possible want
> >> functionality like this. Ever.
> > 
> > The point was that there were no other users currently, so dm-crypt
> > is going to be the only user for the time being.
> > 
> >> If a module wants to be notified - the providing a notifier chain
> >> really seems like the right thing to do...
> > 
> > Well, so please see my last response in this thread. :-)
> 
> So it was below: "Anyway, I guess the "post freeze" new one should be
> enough for now" which doesn't mean I'm really against the notifier.
> Or at least it is not supposed to mean so.  If there's any confusion
> related to that, I'm sorry.
> 
> Thanks,
> Rafael

In that case we are not able to distinguish if computer is going to be 
hibernated or just suspended to RAM.

If we have both notifier (one for suspend and for hibernate) then 
different actions can be configured for suspend and hibernate.

And it makes sense to configure different behaviour for suspend and for 
hibernate. E.g. when you have encrypted partition where is stored 
hibernation image then you do not have to wipe keys before going to do 
hibernation. But for suspend to RAM you may want to wipe them.

-- 
Pali Rohár
pali.rohar@...il.com

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