linux-kernel - Re: [markgross@...ngar.org: [RFC] wake up notifications and suspend blocking (aka more wakelock stuff)]

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Message-ID: <20111008221439.48f30263@notabene.brown>
Date:	Sat, 8 Oct 2011 22:14:39 +1100
From:	NeilBrown <neilb@...e.de>
To:	markgross@...gnar.org
Cc:	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, arve@...roid.com,
	Alan Stern <stern@...land.harvard.edu>,
	amit.kucheria@...aro.org, farrowg@...ibm.com,
	"Dmitry Fink (Palm GBU)" <Dmitry.Fink@...m.com>,
	linux-pm@...ts.linux-foundation.org, khilman@...com,
	Magnus Damm <damm@...nsource.se>, mjg@...hat.com,
	peterz@...radead.org
Subject: Re: [markgross@...ngar.org: [RFC] wake up notifications and suspend
 blocking (aka more wakelock stuff)]

On Sun, 2 Oct 2011 09:44:56 -0700 mark gross <markgross@...gnar.org> wrote:

> resending to wider list for discussion
> ----- Forwarded message from mark gross <markgross@...ngar.org> -----
> 
> Subject: [RFC] wake up notifications and suspend blocking (aka more wakelock stuff)
> Date: Tue, 20 Sep 2011 13:33:05 -0700
> From: mark gross <markgross@...ngar.org>
> To: linux-pm@...ts.linux-foundation.org
> Reply-To: markgross@...gnar.org
> Cc: arve@...roid.com, markgross@...gnar.org, Alan Stern <stern@...land.harvard.edu>, amit.kucheria@...aro.org, farrowg@...ibm.com, "Rafael J. Wysocki" <rjw@...k.pl>
> 
> The following patch set implement an (untested) solution to the
> following problems.
> 
> 1) a method for making a system unable to suspend for critical sections
> of time.

We already have this.  A properly requested suspend (following wakeup_count
protocol) is unable to complete between wakeup_source_activate() and
wake_source_deactivate() - these delimit the critical sections.

What more than this do you need?

If user-space wants to prevent suspend, it just needs some sort of protocol
for talking to the user-space process which follows the correct protocol to
initiate suspend.  That isn't a kernel problem.

> 
> 2) providing a race free method for the acknowledgment of wake event
> processing before re-entry into suspend can happen.

Again, this is a user-space problem.  It is user-space which requests
suspend.  It shouldn't request it until it has checked that there are no wake
events that need processing - and should use the wakeup_count protocol to
avoid races with wakeup events happening after it has checked.

i.e. there is no kernel-space problem to solve here (except for possible
bugs).

NeilBrown

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