From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH] memcg: take reference before releasing rcu_read_lock Date: Fri, 29 Mar 2013 14:48:42 +0400 Message-ID: <5155718A.90108@parallels.com> References: <51556CE9.9060000@huawei.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51556CE9.9060000-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Li Zefan Cc: Michal Hocko , KAMEZAWA Hiroyuki , Johannes Weiner , LKML , Cgroups , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Andrew Morton On 03/29/2013 02:28 PM, Li Zefan wrote: > The memcg is not referenced, so it can be destroyed at anytime right > after we exit rcu read section, so it's not safe to access it. > > To fix this, we call css_tryget() to get a reference while we're still > in rcu read section. > > This also removes a bogus comment above __memcg_create_cache_enqueue(). > Out of curiosity, did you see that happening ? Theoretically, the race you describe seem real, and the fix is sound. Acked-by: Glauber Costa From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx115.postini.com [74.125.245.115]) by kanga.kvack.org (Postfix) with SMTP id 823346B0039 for ; Fri, 29 Mar 2013 06:48:05 -0400 (EDT) Message-ID: <5155718A.90108@parallels.com> Date: Fri, 29 Mar 2013 14:48:42 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH] memcg: take reference before releasing rcu_read_lock References: <51556CE9.9060000@huawei.com> In-Reply-To: <51556CE9.9060000@huawei.com> Content-Type: text/plain; charset="GB2312" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Li Zefan Cc: Michal Hocko , KAMEZAWA Hiroyuki , Johannes Weiner , LKML , Cgroups , linux-mm@kvack.org, Andrew Morton On 03/29/2013 02:28 PM, Li Zefan wrote: > The memcg is not referenced, so it can be destroyed at anytime right > after we exit rcu read section, so it's not safe to access it. > > To fix this, we call css_tryget() to get a reference while we're still > in rcu read section. > > This also removes a bogus comment above __memcg_create_cache_enqueue(). > Out of curiosity, did you see that happening ? Theoretically, the race you describe seem real, and the fix is sound. Acked-by: Glauber Costa -- 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/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754043Ab3C2KsG (ORCPT ); Fri, 29 Mar 2013 06:48:06 -0400 Received: from mx2.parallels.com ([199.115.105.18]:43490 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753051Ab3C2KsE (ORCPT ); Fri, 29 Mar 2013 06:48:04 -0400 Message-ID: <5155718A.90108@parallels.com> Date: Fri, 29 Mar 2013 14:48:42 +0400 From: Glauber Costa User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 MIME-Version: 1.0 To: Li Zefan CC: Michal Hocko , KAMEZAWA Hiroyuki , Johannes Weiner , LKML , Cgroups , , Andrew Morton Subject: Re: [PATCH] memcg: take reference before releasing rcu_read_lock References: <51556CE9.9060000@huawei.com> In-Reply-To: <51556CE9.9060000@huawei.com> Content-Type: text/plain; charset="GB2312" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/29/2013 02:28 PM, Li Zefan wrote: > The memcg is not referenced, so it can be destroyed at anytime right > after we exit rcu read section, so it's not safe to access it. > > To fix this, we call css_tryget() to get a reference while we're still > in rcu read section. > > This also removes a bogus comment above __memcg_create_cache_enqueue(). > Out of curiosity, did you see that happening ? Theoretically, the race you describe seem real, and the fix is sound. Acked-by: Glauber Costa