linux-kernel - Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK

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Date:	Wed, 2 Nov 2011 07:42:57 -0400
From:	Jeff Layton <jlayton@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Oleg Nesterov <oleg@...hat.com>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Steve French <sfrench@...ba.org>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-cifs@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>, trond.myklebust@...app.com,
	linux-nfs@...r.kernel.org
Subject: Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make
 fake_signal_wake_up() wake TASK_KILLABLE tasks too"

On Tue, 1 Nov 2011 14:57:10 -0700
Tejun Heo <tj@...nel.org> wrote:

> Hey, Oleg.
> 
> On Tue, Nov 01, 2011 at 08:46:01PM +0100, Oleg Nesterov wrote:
> > On 11/01, Oleg Nesterov wrote:
> > >
> > > Or we can add TASK_FREEZABLE (like TASK_WAKEKILL), iirc we already
> > > discussed this some time ago. And probably it makes sense to add the
> > > generic wait_event_state().
> > 
> > Forgot to mention. I think that before anything else we need
> > signal_wake_up_state(). For example, note that none of the callers
> > of signal_wake_up(resume => true) in ptrace code wants to wake up
> > the killable task.
> 
> Yeah, agreed for both wait_event_state() and signal_wake_up_state().
> For now, let's go with the count/dont_count.  Can you please write up
> a patch for that?  Jeff, does this seem okay to you?
> 

Let me make sure I understand since I don't have a great grasp of the
freezer internals...

This will set the PF_FREEZER_SKIP flag on the task, which prevents
try_to_freeze_tasks from incrementing the "todo" var for this process
and should let the suspend proceed.

So this really makes try_to_freeze_tasks set PF_FREEZING on the task,
but not get upset that it doesn't actually call try_to_freeze().

Is that sufficient for a process that's just sleeping here?

If so, guess I'll need to respin the NFS/RPC patches for this to do
something similar around the sleeps there since they don't use
wait_event_*.

> For TASK_FREEZABLE, I'm not entirely sure.  Combined with
> wait_event_state(), it can definitely reduce the number of different
> variants of wait_event_*().  Let's see.
> 

wait_event_state() sounds like a wonderful idea regardless of what we
do here.

-- 
Jeff Layton <jlayton@...hat.com>
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