On Thu, 19 Apr 2012 16:54:50 +0800
Sha Zhengju <handai.szj@xxxxxxxxx> wrote:
> From: Sha Zhengju <handai.szj@xxxxxxxxxx>
>
> When the last event is unregistered, there is no need to keep the spare
> array anymore. So free it to avoid memory leak.
How serious is this leak? Is there any way in which it can be used to
consume unbounded amounts of memory?
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4412,6 +4412,12 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
> swap_buffers:
> /* Swap primary and spare array */
> thresholds->spare = thresholds->primary;
> + /* If all events are unregistered, free the spare array */
> + if (!new) {
> + kfree(thresholds->spare);
> + thresholds->spare = NULL;
> + }
> +
> rcu_assign_pointer(thresholds->primary, new);
>
The resulting code is really quite convoluted. Try to read through it
and follow the handling of ->primary and ->spare. Head spins.
What is the protocol here? If ->primary is NULL then ->spare must also
be NULL?
I'll apply the patch, although I don't (yet) have sufficient info to
know which kernels it should be applied to. Perhaps someone could
revisit this code and see if it can be made more straightforward.
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