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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 34A94C43610 for ; Wed, 28 Nov 2018 15:23:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0965020832 for ; Wed, 28 Nov 2018 15:23:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0965020832 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728896AbeK2CZ4 convert rfc822-to-8bit (ORCPT ); Wed, 28 Nov 2018 21:25:56 -0500 Received: from out02.mta.xmission.com ([166.70.13.232]:35255 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728851AbeK2CZz (ORCPT ); Wed, 28 Nov 2018 21:25:55 -0500 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1gS1gt-0004Gx-LG; Wed, 28 Nov 2018 08:23:52 -0700 Received: from 67-3-154-154.omah.qwest.net ([67.3.154.154] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1gS1gt-0000Ak-0W; Wed, 28 Nov 2018 08:23:51 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Oleg Nesterov Cc: =?utf-8?Q?J=C3=BCrg?= Billeter , Andrew Morton , Thomas Gleixner , Kees Cook , Andy Lutomirski , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org References: <20181127225408.7553-1-j@bitron.ch> <20181127225408.7553-2-j@bitron.ch> <20181128144230.GG30395@redhat.com> Date: Wed, 28 Nov 2018 09:23:39 -0600 In-Reply-To: <20181128144230.GG30395@redhat.com> (Oleg Nesterov's message of "Wed, 28 Nov 2018 15:42:31 +0100") Message-ID: <87r2f5gr9g.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-XM-SPF: eid=1gS1gt-0000Ak-0W;;;mid=<87r2f5gr9g.fsf@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=67.3.154.154;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19ZIhrxRrHeEu/P26ASig1IcfQQ3S/A0H0= X-SA-Exim-Connect-IP: 67.3.154.154 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH] prctl: add PR_{GET,SET}_KILL_DESCENDANTS_ON_EXIT X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov writes: > On 11/27, Jürg Billeter wrote: >> >> @@ -704,6 +713,9 @@ static void exit_notify(struct task_struct *tsk, int group_dead) >> struct task_struct *p, *n; >> LIST_HEAD(dead); >> >> + if (group_dead && tsk->signal->kill_descendants_on_exit) >> + walk_process_tree(tsk, kill_descendant_visitor, NULL); > > Well, this is not exactly right, at least this is suboptimal in that > other sub-threads can too call walk_process_tree(kill_descendant_visitor) > later for no reason. Oleg I think I am missing something. Reading kernel/exit.c I see "group_dead = atomic_dec_and_test(&tsk->signal->live)". Which seems like enough to ensure exactly one task/thread calls walk_process_tree. Can you explain what I am missing? Eric