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 588DBC04EB8 for ; Thu, 6 Dec 2018 13:20:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1DD94214C1 for ; Thu, 6 Dec 2018 13:20:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1DD94214C1 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 S1729680AbeLFNUc convert rfc822-to-8bit (ORCPT ); Thu, 6 Dec 2018 08:20:32 -0500 Received: from mx1.redhat.com ([209.132.183.28]:38284 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728953AbeLFNUc (ORCPT ); Thu, 6 Dec 2018 08:20:32 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7050190C78; Thu, 6 Dec 2018 13:20:31 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-116-105.ams2.redhat.com [10.36.116.105]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B9D101001F54; Thu, 6 Dec 2018 13:20:23 +0000 (UTC) From: Florian Weimer To: =?utf-8?Q?J=C3=BCrg?= Billeter Cc: Christian Brauner , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, luto@kernel.org, arnd@arndb.de, ebiederm@xmission.com, serge@hallyn.com, jannh@google.com, akpm@linux-foundation.org, oleg@redhat.com, cyphar@cyphar.com, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, dancol@google.com, timmurray@google.com, linux-man@vger.kernel.org, keescook@chromium.org, tglx@linutronix.de, x86@kernel.org Subject: Re: [PATCH v4] signal: add taskfd_send_signal() syscall References: <20181206121858.12215-1-christian@brauner.io> <87h8fq7s84.fsf@oldenburg2.str.redhat.com> <87pnue6bp2.fsf@oldenburg2.str.redhat.com> <89a6b3a24412d385a816d7d981c60cb1e1bbc0ca.camel@bitron.ch> Date: Thu, 06 Dec 2018 14:20:21 +0100 In-Reply-To: <89a6b3a24412d385a816d7d981c60cb1e1bbc0ca.camel@bitron.ch> (=?utf-8?Q?=22J=C3=BCrg?= Billeter"'s message of "Thu, 06 Dec 2018 14:18:36 +0100") Message-ID: <87efau6bca.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 06 Dec 2018 13:20:32 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Jürg Billeter: > On Thu, 2018-12-06 at 14:12 +0100, Florian Weimer wrote: >> * Jürg Billeter: >> >> > On Thu, 2018-12-06 at 13:30 +0100, Florian Weimer wrote: >> > > * Christian Brauner: >> > > >> > > > /* zombies */ >> > > > Zombies can be signaled just as any other process. No special error will be >> > > > reported since a zombie state is an unreliable state (cf. [3]). >> > > >> > > I still disagree with this analysis. If I know that the target process >> > > is still alive, and it is not, this is a persistent error condition >> > > which can be reliably reported. Given that someone might send SIGKILL >> > > to the process behind my back, detecting this error condition could be >> > > useful. >> > >> > As I understand it, kill() behaves the same way. I think it's good that >> > this new syscall keeps the behavior as close as possible to kill(). >> >> No, kill does not behave in this way because the PID can be reused. >> The error condition is not stable there. > > The PID can't be reused as long as it's a zombie. It can only be reused > when it has been wait()ed for. Or am I misunderstanding something? Hmm, that's a fair point. So the original interface is just broken. Florian