From: Andrew Morton <akpm@linux-foundation.org>
To: Sha Zhengju <handai.szj@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
cgroups@vger.kernel.org, Sha Zhengju <handai.szj@taobao.com>
Subject: Re: [PATCH RESEND] memcg: Free spare array to avoid memory leak
Date: Tue, 1 May 2012 14:03:14 -0700 [thread overview]
Message-ID: <20120501140314.1d7312fb.akpm@linux-foundation.org> (raw)
In-Reply-To: <1334825690-9065-1-git-send-email-handai.szj@taobao.com>
On Thu, 19 Apr 2012 16:54:50 +0800
Sha Zhengju <handai.szj@gmail.com> wrote:
> From: Sha Zhengju <handai.szj@taobao.com>
>
> 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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next prev parent reply other threads:[~2012-05-01 21:03 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-19 8:54 [PATCH RESEND] memcg: Free spare array to avoid memory leak Sha Zhengju
2012-05-01 21:03 ` Andrew Morton [this message]
2012-05-03 3:09 ` Sha Zhengju
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