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Date:	Sat, 18 Oct 2014 23:18:40 +0200
From:	Oleg Nesterov <>
To:	Peter Zijlstra <>
Cc:	Kirill Tkhai <>,
	Kirill Tkhai <>,
	"" <>,
	Ingo Molnar <>,
	Vladimir Davydov <>
Subject: Re: [PATCH] sched/numa: fix unsafe get_task_struct() in

On 10/18, Peter Zijlstra wrote:
> So you worry about the refcount doing 0->1 ? In which case the above is
> still wrong and we should be using atomic_inc_not_zero() in order to
> acquire the reference count.

It is actually worse, please see my reply to Kirill. We simply can't
dereference foreign_rq->curr lockless.

Again, task_struct is only protected by RCU if it was found on a RCU
protected list. rq->curr is not protected by rcu. Perhaps we have to
change this... but this will be a bit unfortunate.


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