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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 1BB97C3F68F for ; Wed, 29 Jan 2020 21:20:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E5C2B20716 for ; Wed, 29 Jan 2020 21:20:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726683AbgA2VUD convert rfc822-to-8bit (ORCPT ); Wed, 29 Jan 2020 16:20:03 -0500 Received: from out02.mta.xmission.com ([166.70.13.232]:37942 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726171AbgA2VUC (ORCPT ); Wed, 29 Jan 2020 16:20:02 -0500 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1iwuki-0007iu-Cc; Wed, 29 Jan 2020 14:20:00 -0700 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1iwukg-0008Hi-II; Wed, 29 Jan 2020 14:20:00 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Sasha Levin Cc: Greg Kroah-Hartman , Thomas Voegtle , linux-kernel@vger.kernel.org, stable@vger.kernel.org, ronnie sahlberg , Christoph =?utf-8?Q?B=C3=B6?= =?utf-8?Q?hmwalder?= , Steve French , Philipp Reisner , David Laight References: <20200128135852.449088278@linuxfoundation.org> <20200128135906.176803329@linuxfoundation.org> <20200129113643.GB5277@kroah.com> <20200129191203.GA2896@sasha-vm> Date: Wed, 29 Jan 2020 15:18:18 -0600 In-Reply-To: <20200129191203.GA2896@sasha-vm> (Sasha Levin's message of "Wed, 29 Jan 2020 14:12:03 -0500") Message-ID: <87o8um0xnp.fsf@x220.int.ebiederm.org> 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-XM-SPF: eid=1iwukg-0008Hi-II;;;mid=<87o8um0xnp.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18bLNmd2EtwKNWhj6tf4CYqtX5mGBaw4Ds= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 4.9 183/271] signal: Allow cifs and drbd to receive their terminating signals X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sasha Levin writes: > On Wed, Jan 29, 2020 at 12:36:43PM +0100, Greg Kroah-Hartman wrote: >>On Wed, Jan 29, 2020 at 12:10:47PM +0100, Thomas Voegtle wrote: >>> On Tue, 28 Jan 2020, Greg Kroah-Hartman wrote: >>> >>> > From: Eric W. Biederman >>> > >>> > [ Upstream commit 33da8e7c814f77310250bb54a9db36a44c5de784 ] >>> > >>> > My recent to change to only use force_sig for a synchronous events >>> > wound up breaking signal reception cifs and drbd. I had overlooked >>> > the fact that by default kthreads start out with all signals set to >>> > SIG_IGN. So a change I thought was safe turned out to have made it >>> > impossible for those kernel thread to catch their signals. >>> > >>> > Reverting the work on force_sig is a bad idea because what the code >>> > was doing was very much a misuse of force_sig. As the way force_sig >>> > ultimately allowed the signal to happen was to change the signal >>> > handler to SIG_DFL. Which after the first signal will allow userspace >>> > to send signals to these kernel threads. At least for >>> > wake_ack_receiver in drbd that does not appear actively wrong. >>> > >>> > So correct this problem by adding allow_kernel_signal that will allow >>> > signals whose siginfo reports they were sent by the kernel through, >>> > but will not allow userspace generated signals, and update cifs and >>> > drbd to call allow_kernel_signal in an appropriate place so that their >>> > thread can receive this signal. >>> > >>> > Fixing things this way ensures that userspace won't be able to send >>> > signals and cause problems, that it is clear which signals the >>> > threads are expecting to receive, and it guarantees that nothing >>> > else in the system will be affected. >>> > >>> > This change was partly inspired by similar cifs and drbd patches that >>> > added allow_signal. >>> > >>> > Reported-by: ronnie sahlberg >>> > Reported-by: Christoph Böhmwalder >>> > Tested-by: Christoph Böhmwalder >>> > Cc: Steve French >>> > Cc: Philipp Reisner >>> > Cc: David Laight >>> > Fixes: 247bc9470b1e ("cifs: fix rmmod regression in cifs.ko caused by force_sig changes") >>> > Fixes: 72abe3bcf091 ("signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force_sig") >>> >>> These two commits come with that release, but... >>> >>> > Fixes: fee109901f39 ("signal/drbd: Use send_sig not force_sig") >>> > Fixes: 3cf5d076fb4d ("signal: Remove task parameter from force_sig") >>> >>> ...these two commits not and were never added to 4.9.y. >>> >>> Are these both really not needed? >> >>I don't think so, do you feel otherwise? > > Both of those commits read as a cleanup to me. I've actually slightly > modified to patch to not need those commits (they were less than trivial > to backport as is). All of these changes were cleanup. Which is why I didn't tag any of them for stable. Not to say that there weren't real problems using force_sig instead of send_sig. force_sig does nothing to ensure the task it is sending signals to won't, and hasn't gone away. Which is why it is a bad idea to use force_sig on anything but current. As I recall drbd used force_sig on a kernel_thread which didn't go away. When fixing the force_sig vs send_sig confusion I didn't realize that some places were using force_sig because they had not enabled receiving the signals they depended on. Which is where allow_kernel_signal comes from. But while using force_sig allow_kernel_signal is not necessary. Eric