linux-kernel - Re: [PATCH 1/6] cgroup_freezer: fix freezer->state setting bug in freezer_change

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Date:	Sun, 4 Sep 2011 20:02:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	matthltc@...ibm.com, rjw@...k.pl, paul@...lmenage.org,
	containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] cgroup_freezer: fix freezer->state setting bug in
	freezer_change_state()

On 09/03, Tejun Heo wrote:
>
> @@ -308,24 +308,24 @@ static int freezer_change_state(struct cgroup *cgroup,
>  	spin_lock_irq(&freezer->lock);
>  
>  	update_if_frozen(cgroup, freezer);
> -	if (goal_state == freezer->state)
> -		goto out;
> -
> -	freezer->state = goal_state;
>  
>  	switch (goal_state) {
>  	case CGROUP_THAWED:
> -		atomic_dec(&system_freezing_cnt);
> +		if (freezer->state != CGROUP_THAWED)
> +			atomic_dec(&system_freezing_cnt);
> +		freezer->state = CGROUP_THAWED;
>  		unfreeze_cgroup(cgroup, freezer);
>  		break;
>  	case CGROUP_FROZEN:
> -		atomic_inc(&system_freezing_cnt);
> +		if (freezer->state == CGROUP_THAWED)
> +			atomic_inc(&system_freezing_cnt);
> +		freezer->state = CGROUP_FREEZING;
>  		retval = try_to_freeze_cgroup(cgroup, freezer);

Cough. Now it doesn't look right to me ;)

If the user write "FROZEN" into the control file, we should not
turn the CGROUP_FROZEN state into CGROUP_FREEZING. Probably this
is harmless, but this looks wrong and this doesn't match the
current behaviour, user-visible change.

Oleg.

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