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=-2.3 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 AF0DDC43A1D for ; Thu, 12 Jul 2018 13:42:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5B78D20BF2 for ; Thu, 12 Jul 2018 13:42:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5B78D20BF2 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 S1732297AbeGLNwB (ORCPT ); Thu, 12 Jul 2018 09:52:01 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:46736 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726782AbeGLNwA (ORCPT ); Thu, 12 Jul 2018 09:52:00 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CEEA04022909; Thu, 12 Jul 2018 13:42:22 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id 4402A111AF0E; Thu, 12 Jul 2018 13:42:21 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 12 Jul 2018 15:42:22 +0200 (CEST) Date: Thu, 12 Jul 2018 15:42:20 +0200 From: Oleg Nesterov To: "Eric W. Biederman" Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, Wen Yang , majiang Subject: Re: [RFC][PATCH 11/11] signal: Ignore all but multi-process signals that come in during fork. Message-ID: <20180712134220.GA15075@redhat.com> References: <877em2jxyr.fsf_-_@xmission.com> <20180711024459.10654-11-ebiederm@xmission.com> <20180711141456.GA6636@redhat.com> <87h8l5g3qi.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87h8l5g3qi.fsf@xmission.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Thu, 12 Jul 2018 13:42:22 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Thu, 12 Jul 2018 13:42:22 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.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 07/11, Eric W. Biederman wrote: > > Oleg Nesterov writes: > > >> - recalc_sigpending(); > >> - if (signal_pending(current)) { > >> + if (read_seqcount_retry(¤t->signal->multi_process_seq, seq) || > >> + fatal_signal_pending(current)) { > >> retval = -ERESTARTNOINTR; > >> goto bad_fork_cancel_cgroup; > > > > So once again, I think this is not right, see the discussion on > > bugzilla. > > I am trying to dig through and understand your concerns. I am having > difficulty understanding your concerns. > > Do the previous patches look good to you? Yes, yes, personally I like 1-10 after a quick glance. I'll try to read this series carefully later, but I don't think I will find something really wrong. > If I understand you correctly. Your concern is that since we added the: > > recalc_sigpending(); > if (signal_pending(current)) > return -ERESTARTNOINTR; > > Other (non-signal) code such as the freezer has come to depend upon that > test. Changing the test in the proposed way will allow the new child to > escape the freezer, as it is not guaranteed the new child will be > frozen. Yes. > > It seems reasonable to look at other things that set TIF_SIGPENDING and > see if any of them are broken by the fork changes. Again, please look at do_signal_stop(). If it was the source of signal_pending(), copy_process() should fail. Or we should update the new thread to participate in group-stop, but then we need to set TIF_SIGPENDING, copy the relevant part of current->jobctl, and increment ->group_stop_count at least. > A practical (and fixable) problem with your patch was that you modified > task->blocked which was then copied to the child. So all children now > would start with all signals being blocked. What are you talking about, this pseudo-code has a lot more bugs ;) OK, at least I certainly agree that this approach needs more changes in copy_process(). > > This also makes another difference in multi-threaded case, a signal with a handler > > sent to a forking process will be re-targeted to another thread which can handle it; > > with your patch this signal will be "blocked" until fork() finishes or until another > > thread gets TIF_SIGPENDING. Not that I think this is that important, > > but still. > > I would not object to wants_signal deciding that a task in the middle of > copy_process does not want signals. This is not enough, we need to signal all in-fork threads... Oleg.