From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E5CC8C3A59C for ; Fri, 16 Aug 2019 06:35:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C17CE2077C for ; Fri, 16 Aug 2019 06:35:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726798AbfHPGfD (ORCPT ); Fri, 16 Aug 2019 02:35:03 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:41388 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726565AbfHPGfC (ORCPT ); Fri, 16 Aug 2019 02:35:02 -0400 Received: from pd9ef1cb8.dip0.t-ipconnect.de ([217.239.28.184] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hyVor-0003Lr-4G; Fri, 16 Aug 2019 08:34:37 +0200 Date: Fri, 16 Aug 2019 08:34:35 +0200 (CEST) From: Thomas Gleixner To: Andrei Vagin cc: Dmitry Safonov , linux-kernel@vger.kernel.org, Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Adrian Reber , Andy Lutomirski , Arnd Bergmann , Christian Brauner , Cyrill Gorcunov , "Eric W. Biederman" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jeff Dike , Oleg Nesterov , Pavel Emelyanov , Shuah Khan , Vincenzo Frascino , containers@lists.linux-foundation.org, criu@openvz.org, linux-api@vger.kernel.org, x86@kernel.org Subject: Re: [PATCHv6 01/36] ns: Introduce Time Namespace In-Reply-To: <20190816061119.GA14312@gmail.com> Message-ID: References: <20190815163836.2927-1-dima@arista.com> <20190815163836.2927-2-dima@arista.com> <20190816061119.GA14312@gmail.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrei, On Thu, 15 Aug 2019, Andrei Vagin wrote: > On Thu, Aug 15, 2019 at 07:19:12PM +0200, Thomas Gleixner wrote: > > > +static int timens_install(struct nsproxy *nsproxy, struct ns_common *new) > > > +{ > > > + struct time_namespace *ns = to_time_ns(new); > > > + > > > + if (!current_is_single_threaded()) > > > + return -EUSERS; > > > + > > > + if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) || > > > + !ns_capable(current_user_ns(), CAP_SYS_ADMIN)) > > > + return -EPERM; > > > + > > > + get_time_ns(ns); > > > + get_time_ns(ns); > > > > Why is this a double get? > > Because we change nsproxy->time_ns and nsproxy->time_ns_for_children. > > Probably, I need to reorgonize the code this way: > > get_time_ns(ns); > put_time_ns(nsproxy->time_ns); > nsproxy->time_ns = ns; > > get_time_ns(ns); > put_time_ns(nsproxy->time_ns_for_children); > nsproxy->time_ns_for_children = ns; That's better. A few comments about refcounting might be useful as well. > > > + put_time_ns(nsproxy->time_ns); > > > + put_time_ns(nsproxy->time_ns_for_children); > > > + nsproxy->time_ns = ns; > > > + nsproxy->time_ns_for_children = ns; > > > + ns->initialized = true; > > > + return 0; > > > +} > > > + > > > +int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *tsk) > > > +{ > > > + struct ns_common *nsc = &nsproxy->time_ns_for_children->ns; > > > + struct time_namespace *ns = to_time_ns(nsc); > > > + > > > + if (nsproxy->time_ns == nsproxy->time_ns_for_children) > > > + return 0; Doesn't this need to take a refcount on fork? Maybe not, but see below. > > > + > > > + get_time_ns(ns); > > > + put_time_ns(nsproxy->time_ns); > > > + nsproxy->time_ns = ns; > > > + ns->initialized = true; > > > > Isn't that one initialized already? > > When we discussed time namespaces last year, we decided that clock > offsets can be set only before any task enters a namespace. > > When a namespace is created, ns->initialized is set to false. When a > task enters the namespace, ns->initialized is set to true. Right. I'm probably just hopelessly confused by this nsproxy->time_ns vs. nsproxy->time_ns_for_children->ns thing. > Namespace clock offsets can be changed only if ns->initialized is false. > > A new task can be forked to a specified time namespace or it can call > setns, so we set ns->initialized to true in timens_on_fork and > timens_install. Some comments explaining that logic above would be really helpful. Thanks, tglx