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=-2.3 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 EB5D8C32751 for ; Wed, 31 Jul 2019 17:41:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CAEE72067D for ; Wed, 31 Jul 2019 17:41:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728318AbfGaRlk (ORCPT ); Wed, 31 Jul 2019 13:41:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41882 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727850AbfGaRlk (ORCPT ); Wed, 31 Jul 2019 13:41:40 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C4B1EC049E32; Wed, 31 Jul 2019 17:41:39 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (ovpn-204-92.brq.redhat.com [10.40.204.92]) by smtp.corp.redhat.com (Postfix) with SMTP id 4EB3660922; Wed, 31 Jul 2019 17:41:37 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 31 Jul 2019 19:41:39 +0200 (CEST) Date: Wed, 31 Jul 2019 19:41:36 +0200 From: Oleg Nesterov To: Adrian Reber Cc: Christian Brauner , Eric Biederman , Pavel Emelianov , Jann Horn , Dmitry Safonov <0x7f454c46@gmail.com>, linux-kernel@vger.kernel.org, Andrei Vagin , Mike Rapoport , Radostin Stoyanov Subject: Re: [PATCH v2 1/2] fork: extend clone3() to support CLONE_SET_TID Message-ID: <20190731174135.GA30225@redhat.com> References: <20190731161223.2928-1-areber@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190731161223.2928-1-areber@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Wed, 31 Jul 2019 17:41:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/31, Adrian Reber wrote: > > Extending clone3() to support CLONE_SET_TID makes it possible restore a > process using CRIU without accessing /proc/sys/kernel/ns_last_pid and > race free (as long as the desired PID/TID is available). I personally like this... but please see the question below. > +struct pid *alloc_pid(struct pid_namespace *ns, int set_tid) > { > struct pid *pid; > enum pid_type type; > @@ -186,12 +186,28 @@ struct pid *alloc_pid(struct pid_namespace *ns) > if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS) > pid_min = RESERVED_PIDS; > > - /* > - * Store a null pointer so find_pid_ns does not find > - * a partially initialized PID (see below). > - */ > - nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min, > - pid_max, GFP_ATOMIC); > + if (set_tid) { > + /* > + * Also fail if a PID != 1 is requested > + * and no PID 1 exists. > + */ > + if ((set_tid >= pid_max) || ((set_tid != 1) && > + (idr_get_cursor(&tmp->idr) <= 1))) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Ah, I forgot to mention... this should work but only because RESERVED_PIDS > 0. How about idr_is_empty() ? But the main question is how it can really help if ns->level > 0, unlikely CRIU will ever need to clone the process with the same pid_nr == set_tid in the ns->parent chain. So may be kernel_clone_args->set_tid should be pid_t __user *set_tid_array? Or I missed something ? Oleg.