Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936593AbXHJPYo (ORCPT ); Fri, 10 Aug 2007 11:24:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759833AbXHJPYd (ORCPT ); Fri, 10 Aug 2007 11:24:33 -0400 Received: from mailhub.sw.ru ([195.214.233.200]:40339 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755114AbXHJPYc (ORCPT ); Fri, 10 Aug 2007 11:24:32 -0400 Message-ID: <46BC7FAC.2080208@openvz.org> Date: Fri, 10 Aug 2007 19:09:32 +0400 From: Pavel Emelyanov User-Agent: Thunderbird 2.0.0.6 (X11/20070728) MIME-Version: 1.0 To: Oleg Nesterov CC: "Serge E. Hallyn" , Andrew Morton , Linux Kernel Mailing List , Linux Containers , "Eric W. Biederman" , "Paul E. McKenney" , devel@openvz.org Subject: Re: [PATCH] Make access to task's nsproxy liter References: <46BAE3A3.7030608@openvz.org> <20070810134003.GA22368@sergelap.austin.ibm.com> <20070810140545.GA74@tv-sign.ru> In-Reply-To: <20070810140545.GA74@tv-sign.ru> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2371 Lines: 62 Oleg Nesterov wrote: > On 08/10, Serge E. Hallyn wrote: >> Quoting Pavel Emelyanov (xemul@openvz.org): >>> +/* >>> + * the namespaces access rules are: >>> + * >>> + * 1. only current task is allowed to change tsk->nsproxy pointer or >>> + * any pointer on the nsproxy itself >>> + * >>> + * 2. when accessing (i.e. reading) current task's namespaces - no >>> + * precautions should be taken - just dereference the pointers >>> + * >>> + * 3. the access to other task namespaces is performed like this >>> + * rcu_read_lock(); >>> + * nsproxy = task_nsproxy(tsk); >>> + * if (nsproxy != NULL) { >>> + * / * >>> + * * work with the namespaces here >>> + * * e.g. get the reference on one of them >>> + * * / >>> + * } / * >>> + * * NULL task_nsproxy() means that this task is >>> + * * almost dead (zombie) >>> + * * / >>> + * rcu_read_unlock(); >> And lastly, I guess that the caller to switch_task_namespaces() has >> to ensure that new_nsproxy either (1) is the init namespace, (2) is a >> brand-new namespace to which noone else has a reference, or (3) the >> caller has to hold a reference to the new_nsproxy across the call to >> switch_task_namespaces(). >> >> As it happens the current calls fit (1) or (2). Again if we happen to >> jump into the game of switching a task into another task's nsproxy, >> we'll need to be mindful of (3) so that new_nsproxy can't be tossed into >> the bin between >> >> if (new) >> get_nsproxy(new); > > 4) Unless tsk == current, get_task_namespaces(tsk) and get_nsproxy(tsk) > are racy even if done under rcu_read_lock(). Yup :) It is already written in comment that only the current is allowed to change its nsproxy. I.e. when switch_task_nsproxy() is called for tsk other than current it's a BUG > Oleg. > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/