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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 5FEEFC433F5 for ; Thu, 6 Sep 2018 22:42:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E51220659 for ; Thu, 6 Sep 2018 22:42:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E51220659 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org 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 S1728186AbeIGDTv convert rfc822-to-8bit (ORCPT ); Thu, 6 Sep 2018 23:19:51 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:50762 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726116AbeIGDTv (ORCPT ); Thu, 6 Sep 2018 23:19:51 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 596A8D0A; Thu, 6 Sep 2018 22:42:09 +0000 (UTC) Date: Thu, 6 Sep 2018 15:42:08 -0700 From: Andrew Morton To: =?ISO-8859-1?Q?J=FCrg?= Billeter Cc: Oleg Nesterov , Thomas Gleixner , Eric Biederman , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/2] prctl: add PR_[GS]ET_KILLABLE Message-Id: <20180906154208.24f397896957116d1a644a3b@linux-foundation.org> In-Reply-To: <20180803144021.56920-2-j@bitron.ch> References: <20180730075241.24002-1-j@bitron.ch> <20180803144021.56920-1-j@bitron.ch> <20180803144021.56920-2-j@bitron.ch> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 3 Aug 2018 16:40:21 +0200 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: > > * 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. > * Many applications do not install handlers for these signals and > thus, job control won't work properly with unmodified applications. > > There are other scenarios besides job control in a shell where > applications rely on the default actions as described in signal(7) and > PID isolation may be useful. This new prctl makes the signal protection > for "init" processes optional, without breaking backward compatibility. This one is above my pay grade. Eric & Oleg: could you please provide input?