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 98972C43142 for ; Tue, 31 Jul 2018 14:39:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 51EA1208A5 for ; Tue, 31 Jul 2018 14:39:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 51EA1208A5 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 S1732483AbeGaQUb (ORCPT ); Tue, 31 Jul 2018 12:20:31 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:60846 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732361AbeGaQUa (ORCPT ); Tue, 31 Jul 2018 12:20:30 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3AA588198B06; Tue, 31 Jul 2018 14:39:52 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id 166701C4C3; Tue, 31 Jul 2018 14:39:50 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 31 Jul 2018 16:39:52 +0200 (CEST) Date: Tue, 31 Jul 2018 16:39:50 +0200 From: Oleg Nesterov To: =?iso-8859-1?Q?J=FCrg?= Billeter Cc: Andrew Morton , Thomas Gleixner , Eric Biederman , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] prctl: add PR_[GS]ET_KILLABLE Message-ID: <20180731143949.GA1890@redhat.com> References: <20180730075241.24002-1-j@bitron.ch> <20180731070337.61004-1-j@bitron.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180731070337.61004-1-j@bitron.ch> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Tue, 31 Jul 2018 14:39:52 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Tue, 31 Jul 2018 14:39:52 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'oleg@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/31, Jürg Billeter wrote: > > PR_SET_KILLABLE clears the SIGNAL_UNKILLABLE flag. This allows > CLONE_NEWPID tasks to restore normal signal behavior, opting out of the > special signal protection for init processes. This prctl does not allow > setting the SIGNAL_UNKILLABLE flag, only clearing. > > The SIGNAL_UNKILLABLE flag, which is implicitly set for tasks cloned > with CLONE_NEWPID, has the effect of ignoring all signals (from > userspace) if the corresponding handler is set to SIG_DFL. The only > exceptions are SIGKILL and SIGSTOP and they are only accepted if raised > from an ancestor namespace. > > SIGINT, SIGQUIT and SIGTSTP are used in job control for ^C, ^\, ^Z. > While a task with the SIGNAL_UNKILLABLE flag could install handlers for > these signals, this is not sufficient to implement a shell that uses > CLONE_NEWPID for child processes: Ah. My question wasn't clear, sorry. Could you explain your use-case? Why a shell wants to use CLONE_NEWPID? And what do we actually want in, say, ^Z case? Just stop the child reaper or may be it would be better to stop the whole pid namespace? > * As SIGSTOP is ignored when raised from the SIGNAL_UNKILLABLE process > itself, it's not possible to implement the stop action in a custom > SIGTSTP handler. Yes. So may be we actually want to change __isig() paths to use SEND_SIG_FORCED (this is not that simple), or perhaps we can change __send_signal() to not drop SIGSTOP sent to itself, or may be we can even introduce SIG_DFL_EVEN_IF_INIT, I dunno. > * Many applications do not install handlers for these signals and > thus, job control won't work properly with unmodified applications. I can't understand this. An application should be changed anyway to do PR_SET_KILLABLE? Let me clarify. I am not arguing with this patch, probably it makes sense in any case. I am just trying to understand your real motivation for this change. > + case PR_SET_KILLABLE: > + if (arg2 != 1 || arg3 || arg4 || arg5) > + return -EINVAL; > + spin_lock_irq(&me->sighand->siglock); > + me->signal->flags &= ~SIGNAL_UNKILLABLE; > + spin_unlock_irq(&me->sighand->siglock); OK, but then you need to change the CLONE_PARENT/SIGNAL_UNKILLABLE check in copy_process(). Oleg.