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

[Balbir Singh]

Paul Menage wrote:
> On 2/19/07, Balbir Singh <balbir@xxxxxxxxxx> 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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