Re: Possible race between cgroup_attach_proc and de_thread, andquestionable code in de_thread.

[Oleg Nesterov]

On 07/28, Paul E. McKenney wrote:
>
> On Thu, Jul 28, 2011 at 11:08:13AM +1000, NeilBrown wrote:
> >
> > I disagree.  It also requires - by virtue of the use of while_each_thread() -
> > that 'g' remains on the list that 't' is walking along.
>
> Doesn't the following code in the loop body deal with this possibilty?
>
> 	/* Exit if t or g was unhashed during refresh. */
> 	if (t->state == TASK_DEAD || g->state == TASK_DEAD)
> 		goto unlock;

This code is completely wrong even if while_each_thread() was fine.

I sent the patch but it was ignored.

	[PATCH] fix the racy check_hung_uninterruptible_tasks()->rcu_lock_break()
	http://marc.info/?l=linux-kernel&m=127688790019041

Oleg.

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