linux-kernel - Re: [PATCH 2/2] mm/linux-next: Fix rcu locking in vm_is

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Date:	Wed, 7 Mar 2012 21:35:29 +0530
From:	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Mark Salter <msalter@...hat.com>,
	linux-next <linux-next@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH 2/2] mm/linux-next: Fix rcu locking in vm_is_stack

On Wed, Mar 7, 2012 at 9:08 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> Once again. You have the task_struct *task. It exits,
> but task->thread_group->next still points to another thread T. Now suppose
> that T exits too. But task->thread_group->next was not changed, it still
> points to T. RCU grace period passes, T is freed.
>
> After that you take rcu_read_lock(), but it is too late! >next points to
> the already freed/reused memory. How can list_first_entry_rcu() help?

Ahh, I completely misunderstood your point. Thanks for the detailed explanation.

> And. Imho it is not good to have the (afaics exactly?) same code in
> mm/nommu.c, even with the same names. Why it is not possible to make
> a single definition?

Yes it is the same code. I put the code in both memory.c and nommu.c
because I thought they fit in there logically. I can find a common
place for it.



-- 
Siddhesh Poyarekar
http://siddhesh.in
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