linux-kernel - Re: [PATCH 0/8] Suspend block api (version 7)

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Date:	Mon, 17 May 2010 22:40:35 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Brian Swetland <swetland@...gle.com>
Subject: Re: [PATCH 0/8] Suspend block api (version 7)

On Monday 17 May 2010, Arve Hjønnevåg wrote:
> 2010/5/16 Rafael J. Wysocki <rjw@...k.pl>:
> > On Friday 14 May 2010, Arve Hjønnevåg wrote:
> >> This patch series adds a suspend-block api that provides the same
> >> functionality as the android wakelock api. This version has some
> >> changes from, or requested by, Rafael. The most notable changes are:
> >> - DEFINE_SUSPEND_BLOCKER and suspend_blocker_register have been added
> >>   for statically allocated suspend blockers.
> >> - suspend_blocker_destroy is now called suspend_blocker_unregister
> >> - The user space mandatory _INIT ioctl has been replaced with an
> >>   optional _SET_NAME ioctl.
> >>
> >> I kept the ack and reviewed by tags on two of the patches even though
> >> there were a few cosmetic changes.
> >
> > I have one more comment, sorry for that.
> >
> > Namely, if /sys/power/policy is set to "opportunistic" and "mem" is written
> > into /sys/power/state and there are no suspend blockers present except for
> > the main blocker (and the blockers used only for statistics), the system won't
> > be able to go out of an infinit suspend-resume loop (or at least it seems
> > so from reading the code).
> >
> > I think we should prevent that from happening somehow.
> >
> 
> It should get out of that loop as soon as someone blocks suspend. If
> someone is constantly aborting suspend without using a suspend blocker
> it will be very inefficient, but it should still work.

Well, the scenario I have in mind is the following.  Someone wants to check
the feature and simply writes "opportunistic" to /sys/power/policy and "mem" to
/sys/power/state without any drivers or apps that use suspend blockers.

How in that case is the system supposed to break out of the suspend-resume loop
resulting from this?  I don't see right now, because the main blocker is
inactive, there are no other blockers that can be activated and it is next to
impossible to write to /sys/power/state again.

Rafael
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