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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 58190C04EB8 for ; Fri, 30 Nov 2018 10:33:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 17E342146D for ; Fri, 30 Nov 2018 10:33:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 17E342146D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.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 S1726765AbeK3VmX (ORCPT ); Fri, 30 Nov 2018 16:42:23 -0500 Received: from mx1.redhat.com ([209.132.183.28]:16297 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726507AbeK3VmX (ORCPT ); Fri, 30 Nov 2018 16:42:23 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E6FEF80F7D; Fri, 30 Nov 2018 10:33:32 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.12]) by smtp.corp.redhat.com (Postfix) with SMTP id 410C15D736; Fri, 30 Nov 2018 10:33:30 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 30 Nov 2018 11:33:32 +0100 (CET) Date: Fri, 30 Nov 2018 11:33:30 +0100 From: Oleg Nesterov To: =?iso-8859-1?Q?J=FCrg?= Billeter Cc: "Eric W. Biederman" , Andrew Morton , Thomas Gleixner , Kees Cook , Andy Lutomirski , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] prctl: add PR_{GET,SET}_KILL_DESCENDANTS_ON_EXIT Message-ID: <20181130103329.GB23670@redhat.com> References: <20181127225408.7553-1-j@bitron.ch> <20181127225408.7553-2-j@bitron.ch> <20181128144230.GG30395@redhat.com> <87r2f5gr9g.fsf@xmission.com> <20181129123409.GA10645@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 30 Nov 2018 10:33:33 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/29, Jürg Billeter wrote: > > On Thu, 2018-11-29 at 13:34 +0100, Oleg Nesterov wrote: > > To me it would be more clean to call walk_process_tree(kill_descendant_visitor) > > unconditionally in find_new_reaper() right before "if (has_child_subreaper)", but > > then we will need to shift read_lock(tasklist) from walk_process_tree(). > > Yes, that's the reason why I added the call before the tasklist lock. > Let me know if you want me to move the read lock from > walk_process_tree() to PR_SET_CHILD_SUBREAPER (the only caller) > instead. I am fine either way. We can do this later, lets keep your patch simple. > > So I think the patch is mostly fine, the only problem I can see is that > > PR_SET_KILL_DESCENDANTS_ON_EXIT can race with PR_SET_CHILD_SUBREAPER, they both > > need to update the bits in the same word. > > Good point. I'll make it a regular bool instead of a bitfield for v2, Agreed, > unless you have another approach in mind to fix this. Well, I think that is_child_subreaper/has_child_subreaper and the new kill_descendants_on_exit should live in signal->flags, but we need some cleanups to make this possible, so I agree with the boolean. Oleg.