linux-kernel - Re: [PATCH 4/4] cgroup: always lock threadgroup during migration

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Message-ID: <20110918174117.GB2384@redhat.com>
Date:	Sun, 18 Sep 2011 19:41:17 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <htejun@...il.com>
Cc:	rjw@...k.pl, paul@...lmenage.org, lizf@...fujitsu.com,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, fweisbec@...il.com,
	matthltc@...ibm.com, akpm@...ux-foundation.org,
	Tejun Heo <tj@...nel.org>, Paul Menage <menage@...gle.com>
Subject: Re: [PATCH 4/4] cgroup: always lock threadgroup during migration

On 09/05, Tejun Heo wrote:
>
> * Remove -ESRCH failure path from cgroup_task_migrate().  With the
>   above changes, it's guaranteed to be called only for live tasks.

I think you can remove another similar check,

> @@ -2044,6 +2044,10 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
>  	tsk = leader;
>  	i = 0;
>  	do {
> +		/* @tsk either already exited or can't exit until the end */
> +		if (tsk->flags & PF_EXITING)
> +			continue;
> +
>  		/* as per above, nr_threads may decrease, but not increase. */
>  		BUG_ON(i >= group_size);
>  		get_task_struct(tsk);

And then cgroup_attach_proc() does

	for (i = 0; i < group_size; i++) {
		...
		task_lock(tsk);
		if (tsk->flags & PF_EXITING) {
			task_unlock(tsk);
			continue;

Afaics, this is no longer needed.

Oleg.

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