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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 E9BFBC32750 for ; Tue, 13 Aug 2019 14:30:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD1C42067D for ; Tue, 13 Aug 2019 14:30:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729539AbfHMOa1 (ORCPT ); Tue, 13 Aug 2019 10:30:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50711 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729304AbfHMOa1 (ORCPT ); Tue, 13 Aug 2019 10:30:27 -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 35F5C30605EF; Tue, 13 Aug 2019 14:30:27 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 04EA56092F; Tue, 13 Aug 2019 14:30:24 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 13 Aug 2019 16:30:26 +0200 (CEST) Date: Tue, 13 Aug 2019 16:30:24 +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 v6 1/2] fork: extend clone3() to support setting a PID Message-ID: <20190813143023.GC6971@redhat.com> References: <20190812200939.23784-1-areber@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190812200939.23784-1-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 [10.5.110.46]); Tue, 13 Aug 2019 14:30:27 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/12, Adrian Reber wrote: > > The main motivation to add set_tid to clone3() is CRIU. > > To restore a process with the same PID/TID CRIU currently uses > /proc/sys/kernel/ns_last_pid. It writes the desired (PID - 1) to > ns_last_pid and then (quickly) does a clone(). This works most of the > time, but it is racy. It is also slow as it requires multiple syscalls. > > Extending clone3() to support 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). > > This clone3() extension places the same restrictions (CAP_SYS_ADMIN) > on clone3() with set_tid as they are currently in place for ns_last_pid. > > Signed-off-by: Adrian Reber Reviewed-by: Oleg Nesterov