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

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Message-ID: <CAJZ5v0h-0Jo7A0hmPSfHcZbkRU7wKwVtSqTCCwX1rs=iBE9G5g@mail.gmail.com>
Date:	Wed, 22 Jul 2015 01:00:10 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	NeilBrown <neilb@...e.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pali Rohár <pali.rohar@...il.com>,
	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

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. :-)

Thanks,
Rafael
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