From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751362AbdEBQeX (ORCPT ); Tue, 2 May 2017 12:34:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54110 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751165AbdEBQeR (ORCPT ); Tue, 2 May 2017 12:34:17 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 19EB32826B Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=oleg@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 19EB32826B Date: Tue, 2 May 2017 18:33:25 +0200 From: Oleg Nesterov To: Kirill Tkhai Cc: serge@hallyn.com, ebiederm@xmission.com, agruenba@redhat.com, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, paul@paul-moore.com, viro@zeniv.linux.org.uk, avagin@openvz.org, linux-fsdevel@vger.kernel.org, mtk.manpages@gmail.com, akpm@linux-foundation.org, luto@amacapital.net, gorcunov@openvz.org, mingo@kernel.org, keescook@chromium.org Subject: Re: [PATCH 2/2] pid_ns: Introduce ioctl to set vector of ns_last_pid's on ns hierarhy Message-ID: <20170502163324.GA25036@redhat.com> References: <149245014695.17600.12640895883798122726.stgit@localhost.localdomain> <149245057248.17600.1341652606136269734.stgit@localhost.localdomain> <20170426155352.GA12131@redhat.com> <785e1986-da03-72aa-06c0-234ed2dbc0fd@virtuozzo.com> <20170427161255.GA19350@redhat.com> <20170427162254.GB19579@redhat.com> <43249645-f621-511e-dfa8-7bd78c547d2c@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <43249645-f621-511e-dfa8-7bd78c547d2c@virtuozzo.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 02 May 2017 16:34:16 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org sorry for delay, vacation... On 04/28, Kirill Tkhai wrote: > > On 27.04.2017 19:22, Oleg Nesterov wrote: > > > > Ah, OK, I didn't notice the ns->child_reaper check in pidns_for_children_get(). > > > > But note that it doesn't need tasklist_lock too. > > Hm, are there possible strange situations with memory ordering, when we see > ns->child_reaper of already died ns, which was placed in the same memory? > Do we have to use some memory barriers here? Could you spell please? I don't understand your concerns... I don't see how, say, static struct ns_common *pidns_for_children_get(struct task_struct *task) { struct ns_common *ns = NULL; struct pid_namespace *pid_ns; task_lock(task); if (task->nsproxy) { pid_ns = task->nsproxy->pid_ns_for_children; if (pid_ns->child_reaper) { ns = &pid_ns->ns; get_pid_ns(ns); } } task_unlock(task); return ns; } can be wrong. It also looks more clean to me. ->child_reaper is not stable without tasklist, it can be dead/etc, but we do not care? Oleg.