linux-kernel - Re: [RFC PATCH] PM, freezer: Don't thaw when it's intended frozen processes

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Date:	Fri, 8 May 2015 09:04:26 +0900
From:	Kyungmin Park <kmpark@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"\\Rafael J. Wysocki\\" <rjw@...ysocki.net>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH] PM, freezer: Don't thaw when it's intended frozen processes

On Fri, May 8, 2015 at 12:42 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Thu, May 07, 2015 at 03:45:57PM +0900, Kyungmin Park wrote:
>> From: Kyungmin Park <kyungmin.park@...sung.com>
>>
>> Some platform uses freezer cgroup for speicial purpose to schedule out some applications. but after suspend & resume, these processes are thawed and running.
>
> They shouldn't be able to leave the freezer tho.  Resuming does wake
> up all tasks but freezing() test would still evaulate to true for the
> ones frozen by cgroup freezer and they will stay inside the freezer.
>
>> but it's inteneded and don't need to thaw it.
>>
>> To avoid it, does it possible to modify resume code and don't thaw it when resume? does it resonable?
>
> I need to think more about it but as an *optimization* we can add
> freezing() test before actually waking tasks up during resume, but can
> you please clarify what you're seeing?

The mobile application has life cycle and one of them is 'suspend'
state. it's different from 'pause' or 'background'.
if there are some application and enter go 'suspend' state. all
behaviors are stopped and can't do anything. right it's suspended. but
after system suspend & resume, these application is thawed and
running. even though system know it's suspended.

We made some test application, print out some message within infinite
loop. when it goes 'suspend' state. nothing is print out. but after
system suspend & resume, it prints out again. that's not desired
behavior. and want to address it.

frozen user processes should be remained as frozen while system
suspend & resume.

Thank you,
Kyungmin Park
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