linux-kernel - Re: [PATCH pm-freezer 1/4] cgroup_freezer: fix freezer->state setting bug in freezer_change

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Date:	Fri, 2 Sep 2011 18:58:39 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Tejun Heo <tj@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Paul Menage <paul@...lmenage.org>,
	containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH pm-freezer 1/4] cgroup_freezer: fix freezer->state
	setting bug in freezer_change_state()

On 09/01, Matt Helsley wrote:
>
> On Wed, Aug 31, 2011 at 12:21:07PM +0200, Tejun Heo wrote:
> >  	case CGROUP_FROZEN:
> > -		atomic_inc(&system_freezing_cnt);
> > -		retval = try_to_freeze_cgroup(cgroup, freezer);
> > +		if (freezer->state == CGROUP_THAWED) {
> > +			freezer->state = CGROUP_FREEZING;
> > +			atomic_inc(&system_freezing_cnt);
> > +			retval = try_to_freeze_cgroup(cgroup, freezer);
>
> This still doesn't look quite right. If the cgroup is FREEZING it should
> also call try_to_freeze_cgroup(). I think this is what's needed:
>
> 		if (freezer->state == CGROUP_THAWED)
> 			atomic_inc(&system_freezing_cnt);
> 		freezer->state = CGROUP_FREEZING;
> 		retval = try_to_freeze_cgroup(cgroup, freezer);

This is what I mentioned before, to me this looks like a win.

Why do we need try_to_freeze_cgroup() in this case? "for safety"
could actually mean "hide the bug" ;)


But I agree either way. Rafael, I think 1-4 are fine, but I think
we need the simple 5/4, will send in a minute...

Oleg.

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