From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx127.postini.com [74.125.245.127]) by kanga.kvack.org (Postfix) with SMTP id 9C09B6B004D for ; Tue, 1 May 2012 17:03:17 -0400 (EDT) Date: Tue, 1 May 2012 14:03:14 -0700 From: Andrew Morton Subject: Re: [PATCH RESEND] memcg: Free spare array to avoid memory leak Message-Id: <20120501140314.1d7312fb.akpm@linux-foundation.org> In-Reply-To: <1334825690-9065-1-git-send-email-handai.szj@taobao.com> References: <1334825690-9065-1-git-send-email-handai.szj@taobao.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Sha Zhengju Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, Sha Zhengju On Thu, 19 Apr 2012 16:54:50 +0800 Sha Zhengju wrote: > From: Sha Zhengju > > 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org