linux-kernel - Re: [ckrm-tech] [RFC][PATCH][2/4] Add RSS accounting and control

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Date:	Mon, 19 Feb 2007 19:40:06 +0530
From:	Balbir Singh <balbir@...ibm.com>
To:	Paul Menage <menage@...gle.com>
CC:	vatsa@...ibm.com, ckrm-tech@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, xemul@...ru, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	svaidy@...ux.vnet.ibm.com, devel@...nvz.org
Subject: Re: [ckrm-tech] [RFC][PATCH][2/4] Add RSS accounting and control

Paul Menage wrote:
> On 2/19/07, Balbir Singh <balbir@...ibm.com> wrote:
>>> More worrisome is the potential for use-after-free.  What prevents the
>>> pointer at mm->container from referring to freed memory after we're dropped
>>> the lock?
>>>
>> The container cannot be freed unless all tasks holding references to it are
>> gone,
> 
> ... or have been moved to other containers. If you're not holding
> task->alloc_lock or one of the container mutexes, there's nothing to
> stop the task being moved to another container, and the container
> being deleted.
> 
> If you're in an RCU section then you can guarantee that the container
> (that you originally read from the task) and its subsystems at least
> won't be deleted while you're accessing them, but for accounting like
> this I suspect that's not enough, since you need to be adding to the
> accounting stats on the correct container. I think you'll need to hold
> mm->container_lock for the duration of memctl_update_rss()
> 
> Paul
> 

Yes, that sounds like the correct thing to do.

-- 
	Warm Regards,
	Balbir Singh
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