linux-kernel - Re: cpuset attach_task to touch per-cpu kernel threads?

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Message-ID: <20070622171634.GA21543@linux.vnet.ibm.com>
Date:	Fri, 22 Jun 2007 22:46:34 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Paul Jackson <pj@....com>
Cc:	mingo@...e.hu, clameter@....com, linux-kernel@...r.kernel.org,
	dino@...ibm.com, akpm@...ux-foundation.org
Subject: Re: cpuset attach_task to touch per-cpu kernel threads?

On Thu, Jun 21, 2007 at 10:51:52AM -0700, Paul Jackson wrote:
> The only problem comes with kernel tasks that are pinned to less than
> the entire system, and that are in the top cpuset.

That again is not fool-proof. What if kernel-tasks change their cpu affinity
after we have done the is_pinned_kernel_thread() test? Ideally they
should not, but one never knows!

IMHO we simply should not allow kernel threads to move out of top-cpuset
(unless you know of a good reason where we may want to move them).


int cpuset_can_attach()
{

	int is_kthread = !tsk->mm || (tsk->flags & PF_BORROWED_MM);

	...

 	/* Don't moved pinned kernel threads out of top cpuset */
 	if (is_kthread && oldcs == &top_cpuset && cs != oldcs) {
                 task_unlock(tsk);
                 mutex_unlock(&callback_mutex);
                 put_task_struct(tsk);
 		return -EINVAL;
 	}

}


What do you think?

-- 
Regards,
vatsa
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