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,URIBL_BLOCKED,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 897EBC07E85 for ; Fri, 7 Dec 2018 16:49:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 512492081C for ; Fri, 7 Dec 2018 16:49:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 512492081C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=hallyn.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 S1726142AbeLGQtc (ORCPT ); Fri, 7 Dec 2018 11:49:32 -0500 Received: from mail.hallyn.com ([178.63.66.53]:40506 "EHLO mail.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726018AbeLGQtb (ORCPT ); Fri, 7 Dec 2018 11:49:31 -0500 Received: by mail.hallyn.com (Postfix, from userid 1001) id 296CBDE8; Fri, 7 Dec 2018 10:49:28 -0600 (CST) Date: Fri, 7 Dec 2018 10:49:28 -0600 From: "Serge E. Hallyn" To: Christian Brauner Cc: Daniel Colascione , "Serge E. Hallyn" , "Eric W. Biederman" , linux-kernel , Linux API , Andy Lutomirski , Arnd Bergmann , Jann Horn , Andrew Morton , Oleg Nesterov , Aleksa Sarai , Al Viro , Linux FS Devel , Tim Murray , linux-man , Kees Cook , Florian Weimer , tglx@linutronix.de, x86@kernel.org Subject: Re: [PATCH v4] signal: add taskfd_send_signal() syscall Message-ID: <20181207164928.GB972@mail.hallyn.com> References: <871s6u9z6u.fsf@xmission.com> <20181206213152.gvci7ijr3dokew7w@brauner.io> <87o99y72gi.fsf@xmission.com> <20181206223948.gyfdtkgbhtozmpsp@brauner.io> <20181206231742.xxi4ghn24z4h2qki@brauner.io> <20181207003124.GA11160@mail.hallyn.com> <20181207005917.GA11302@mail.hallyn.com> <20181207015423.4miorx43l3qhppfz@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181207015423.4miorx43l3qhppfz@brauner.io> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 07, 2018 at 02:54:25AM +0100, Christian Brauner wrote: > On Thu, Dec 06, 2018 at 05:39:18PM -0800, Daniel Colascione wrote: > > On Thu, Dec 6, 2018 at 4:59 PM Serge E. Hallyn wrote: > > > > > > On Thu, Dec 06, 2018 at 04:34:54PM -0800, Daniel Colascione wrote: > > > > On Thu, Dec 6, 2018 at 4:31 PM Serge E. Hallyn wrote: > > > > > > > > > > On Fri, Dec 07, 2018 at 12:17:45AM +0100, Christian Brauner wrote: > > > > > > On Thu, Dec 06, 2018 at 11:39:48PM +0100, Christian Brauner wrote: > > > > > > > On Thu, Dec 06, 2018 at 03:46:53PM -0600, Eric W. Biederman wrote: > > > > > > > > Christian Brauner writes: > > > > > > > > > > > > > > > > >> Your intention is to add the thread case to support pthreads once the > > > > > > > > >> process case is sorted out. So this is something that needs to be made > > > > > > > > >> clear. Did I miss how you plan to handle threads? > > > > > > > > > > > > > > > > > > Yeah, maybe you missed it in the commit message [2] which is based on a > > > > > > > > > discussion with Andy [3] and Arnd [4]: > > > > > > > > > > > > > > > > Looking at your references I haven't missed it. You are not deciding > > > > > > > > anything as of yet to keep it simple. Except you are returning > > > > > > > > EOPNOTSUPP. You are very much intending to do something. > > > > > > > > > > > > > > That was clear all along and was pointed at every occassion in the > > > > > > > threads. I even went through the hazzle to give you all of the > > > > > > > references when there's lore.kernel.org. > > > > > > > > > > > > > > > > > > > > > > > Decide. Do you use the flags parameter or is the width of the > > > > > > > > target depending on the flags. > > > > > > > > > > > > Ok, let's try to be constructive. I understand the general concern for > > > > > > the future so let's put a contract into the commit message stating that > > > > > > the width of the target aka *what is signaled* will be based on a flag > > > > > > parameter if we ever extend it: > > > > > > > > > > > > taskfd_send_signal(fd, SIGSTOP, NULL, TASKFD_PGID); > > > > > > taskfd_send_signal(fd, SIGSTOP, NULL, TASKFD_TID); > > > > > > > > > > > > with the current default being > > > > > > > > > > > > taskfd_send_signal(fd, SIGSTOP, NULL, TASKFD_PID); > > > > > > > > > > > > This seems to me the cleanest solution as we only use one type of file > > > > > > descriptor. Can everyone be on board with this? If so I'm going to send > > > > > > out a new version of the patch. > > > > > > > > > > > > Christian > > > > > > > > > > I'm on board with this, but I think you need to also clarify what exactly > > > > > the fd stands for. I think that (a) userspace should not have to care > > > > > about the struct pid implementation, and so (b) the procfd should stand > > > > > for all the pids. So when taskfd_send_signal(fd, SIGSTOP, NULL, TASKFD_PGID) > > > > > becomes implemented, then open(/proc/5) will pin all three pids, as will > > > > > open(/proc/5/task/6). > > > > > > > > This change doesn't "pin" any PID, and it makes no sense to make a > > > > process FD stand for all its threads. What does that even mean? > > > > > > Currently the patch relies on the procfd inode saving a copy to the PIDTYPE_PID > > > pid. > > > > struct pid doesn't have a type field. The interpretation depends on > > the caller's use of the struct pid, and in the current path, that's > > PIDTYPE_PID. What, specifically, is wrong with the current approach? > > > > > I'm not sure offhand, can it go to the PIDTYPE_PGID from that after the > > > task has died, or not? I didn't think so. If it can then great. > > > > You're arguing that something that does, in fact, work, is somehow > > broken in some unspecified way. The kill_pid_info lookup works fine. > > What, specifically, is wrong with the semantics as implemented? > > > > > The point is (a) these are details which should not have to bother userspace, > > > > These details *don't* bother userspace. > > > > You're raising concerns that are either imaginary or long-since > > addressed. Does the patch cause some kind of maintenance burden? No, > > it doesn't, not moreso than any other piece of code. Does the > > interface have unclear semantics? No, it clearly sends a signal to a > > process, just like kill. Does the patch expose kernel implementation > > details? No, it doesn't, because the interface is simply not defined > > in terms of these details. Do we need to change how signal delivery > > works? No, because if it's fine for kill, it's fine for this facility, > > and if some future signal cleanup separates the cases more, that > > cleanup can change this code as well. > > > > The change is well-documented, simple, extensible, and addresses an > > actual problem. Every legitimate technical criticism has now been > > addressed. I don't understand where this opposition is coming from, > > since the objections refer to nothing that's actually in the patch or > > exposed to the user. > > > > > and (b) how to decide who we're sending the signal to (tid/pid/pgid) should > > > be specified in precisely one way. So either a flag, or comign from the type > > > of fd that was opened. > > > > You can't send signals to a thread with the current patch. There's no > > ambiguity in providing zero ways to do something. > > So Serge's point is not about changing the current patch. What he's Right, I'm an ack on the patch. As is no changes are needed. > basically saying is: If we are expected to state how we were to extend > this syscall in the future which Serge and I figured is currently Eric's > only remaining objection then: > - flags are a good way to go (I agree) > - there's a concrete way how to do this by stashing the relevent struct > pids for PIDTYPE_PID, PIDTYPE_TGID, PIDTYPE_PGID in file->private_data > which can then be retrieved in taskfd_send_signal() > There is not intent nor requirement to do this right now. What we have > right now is fine for a start, I agree! But here's how we go forward if > we ever need to! :) > > Christian